1 00:00:00,040 --> 00:00:03,120 Welcome back to The Deep Dive, the only place engineered to 2 00:00:03,120 --> 00:00:06,040 give you a comprehensive understanding of an entire 3 00:00:06,040 --> 00:00:10,640 year's worth of challenging material, delivered in about the 4 00:00:10,640 --> 00:00:13,320 time it takes to perfectly procrastinate before a major 5 00:00:13,320 --> 00:00:15,840 exam. We know exactly why you've 6 00:00:15,840 --> 00:00:18,800 joined us today. You're a second year BSc student 7 00:00:19,360 --> 00:00:22,000 and you're looking down the barrel of an Inorganic Chemistry 8 00:00:22,000 --> 00:00:25,520 review. You need the ultimate high speed 9 00:00:25,520 --> 00:00:27,960 conceptual CHEAT SHEET. That's absolutely right. 10 00:00:28,440 --> 00:00:32,840 Our mission today is a targeted top speed recap of your entire 11 00:00:32,840 --> 00:00:34,760 inorganic course. You've been bombarded with 12 00:00:34,760 --> 00:00:37,400 information, you know, covering everything from individual 13 00:00:37,400 --> 00:00:39,800 electrons to macroscopic crystal lattices. 14 00:00:40,240 --> 00:00:42,920 And the goal now isn't just recalling individual facts, it's 15 00:00:42,920 --> 00:00:45,840 about synthesizing that knowledge, understanding how the 16 00:00:45,840 --> 00:00:48,800 foundational properties of the atom, how they govern most 17 00:00:48,800 --> 00:00:53,040 complex catalytic cycles. We are unifying your 4 core 18 00:00:53,040 --> 00:00:54,880 learning pillars. This course is a beast. 19 00:00:55,040 --> 00:00:57,960 What 4 pillars did we distill from your source material to 20 00:00:57,960 --> 00:01:01,200 build this unified framework? Well, we organized the material 21 00:01:01,200 --> 00:01:03,120 logically. We begin at the smallest scale 22 00:01:03,120 --> 00:01:06,280 with module one, the atomic foundation, focusing on 23 00:01:06,280 --> 00:01:10,200 periodicity and bonding trends. That understanding of the atom 24 00:01:10,200 --> 00:01:13,200 that allows us to predict how things interact in module 2. 25 00:01:14,000 --> 00:01:19,040 Chemical reactivity covering acids, bases and the 26 00:01:19,040 --> 00:01:22,000 quantitative thermodynamics of redox chemistry. 27 00:01:22,080 --> 00:01:24,840 And once we know how atoms and simple ions behave, we can look 28 00:01:24,840 --> 00:01:28,800 at complex structured materials. Precisely, Module 3 focuses on 29 00:01:28,800 --> 00:01:32,080 the architecture of solids, which moves us into crystal 30 00:01:32,080 --> 00:01:35,760 packing, lattice energy, electronic band structure and 31 00:01:35,760 --> 00:01:38,640 modern materials like semiconductors and and quantum 32 00:01:38,640 --> 00:01:40,200 dots. And then the final piece. 33 00:01:40,240 --> 00:01:42,560 Finally, we bring it all together to look at solution 34 00:01:42,560 --> 00:01:45,920 chemistry in high detail with Module 4 coordination and 35 00:01:45,920 --> 00:01:49,120 organometallic dynamics, examining complex stability, 36 00:01:49,240 --> 00:01:51,680 reaction mechanisms and catalysis cycles. 37 00:01:51,680 --> 00:01:55,000 The key then is seeing the link. How does effective nuclear 38 00:01:55,000 --> 00:01:57,880 charge, which is a module 1 concept, influence something 39 00:01:57,880 --> 00:02:00,760 like the stabilization of a high oxidation state in a 40 00:02:00,760 --> 00:02:03,640 coordination complex, which is all the way in module 4? 41 00:02:03,800 --> 00:02:05,080 That's what we need to eliminate. 42 00:02:05,160 --> 00:02:07,160 OK, let's unpack this, starting right at the beginning. 43 00:02:07,560 --> 00:02:09,039 The atomic foundation. Let's do it. 44 00:02:09,039 --> 00:02:11,920 So the periodic table, it's not just a poster on the wall. 45 00:02:12,040 --> 00:02:14,640 Not at all. It is the ultimate organizing 46 00:02:14,640 --> 00:02:17,640 principle of chemistry. Its structure allows us to 47 00:02:17,640 --> 00:02:20,840 predict elemental behavior across the whole spectrum by 48 00:02:20,840 --> 00:02:23,920 understanding systematic predictable variations, 49 00:02:23,920 --> 00:02:27,320 periodicity in their properties. And the single concept that 50 00:02:27,320 --> 00:02:32,800 governs nearly all those trends is effective nuclear charge ZF. 51 00:02:33,400 --> 00:02:37,400 We are taught that Z is the proton count, but ZF is what 52 00:02:37,400 --> 00:02:39,840 actually matters for reactivity. Why? 53 00:02:40,440 --> 00:02:42,040 Why don't we just use the proton count? 54 00:02:42,080 --> 00:02:44,240 That's an excellent question, and it cuts to the core of 55 00:02:44,240 --> 00:02:47,200 orbital mechanics. We don't use Z because electrons 56 00:02:47,200 --> 00:02:50,640 are not simple planetary orbits. Electrons in inner shells, 57 00:02:50,640 --> 00:02:53,680 specifically the core electrons, efficiently shield the outer 58 00:02:54,000 --> 00:02:57,360 valence electrons from the full strong positive pole of the 59 00:02:57,360 --> 00:02:59,000 nucleus. So ZF is what the valence 60 00:02:59,000 --> 00:03:02,600 electron actually experiences. It's the net positive charge it 61 00:03:02,600 --> 00:03:05,800 feels. Yes, the shielding constant S 62 00:03:05,840 --> 00:03:09,160 accounts for two things. The nearly complete shielding by 63 00:03:09,160 --> 00:03:12,640 core electrons and the incomplete shielding from other 64 00:03:12,640 --> 00:03:15,440 electrons in the same shell. That electron electron 65 00:03:15,440 --> 00:03:16,480 repulsion. Right. 66 00:03:16,720 --> 00:03:20,080 So we use the formula ZF equals Z -, s. 67 00:03:20,520 --> 00:03:23,880 As we move across a period, Z increases by one each time, but 68 00:03:23,880 --> 00:03:27,400 the new electron enters the same shell, adding only marginally to 69 00:03:27,400 --> 00:03:31,320 S Therefore ZF increases significantly left to right, 70 00:03:31,520 --> 00:03:33,280 pulling the valence cloud inward. 71 00:03:33,520 --> 00:03:36,840 That increasing pull explains why atoms shrink left to right. 72 00:03:38,000 --> 00:03:41,200 When we talk about size, we have to be meticulous because atomic 73 00:03:41,200 --> 00:03:43,560 size is defined differently depending on the bonding 74 00:03:43,560 --> 00:03:45,760 context. Indeed, we have three main 75 00:03:45,760 --> 00:03:47,960 categories. For metals which form large 76 00:03:47,960 --> 00:03:50,080 lattice structures, we use the metallic radius. 77 00:03:50,160 --> 00:03:52,800 Which is what, half the distance between two atoms in the metal? 78 00:03:52,880 --> 00:03:55,240 Half the distance between the centers of nearest neighbor 79 00:03:55,240 --> 00:03:56,640 atoms in the solid. Yeah. 80 00:03:57,160 --> 00:03:59,520 And crucially, this value is highly dependent on the 81 00:03:59,520 --> 00:04:02,360 coordination number, and tables usually standardize this. 82 00:04:02,360 --> 00:04:05,360 For a coordination number of 12 reflecting a close packed 83 00:04:05,360 --> 00:04:08,680 environment and for non metals it's the radius. 84 00:04:08,840 --> 00:04:11,800 The covalent radius is half the intranuclear distance between 85 00:04:11,800 --> 00:04:15,560 two identical neighboring atoms in a molecular compound, but 86 00:04:15,560 --> 00:04:17,560 it's vital to remember the new ones. 87 00:04:17,560 --> 00:04:20,240 Here. The radius is context dependent. 88 00:04:20,240 --> 00:04:22,680 How so? A covalent radius measured for a 89 00:04:22,680 --> 00:04:26,560 single bond, like a carbon carbon single bond will always 90 00:04:26,560 --> 00:04:29,280 be longer than the radius measured for the same element 91 00:04:29,280 --> 00:04:32,360 involved in a multiple bond, like a carbon carbon double 92 00:04:32,360 --> 00:04:33,920 bond. Because the extra electron 93 00:04:33,920 --> 00:04:36,480 density pulls the nuclei closer. Exactly. 94 00:04:36,480 --> 00:04:39,520 It squeezes them together. Trickiest definition though is 95 00:04:39,520 --> 00:04:42,400 ionic radii. Because we can't measure an 96 00:04:42,400 --> 00:04:46,320 ion's radius in isolation, we have to essentially guess where 97 00:04:46,320 --> 00:04:49,480 the electron density boundary lies between the Caitian and 98 00:04:49,480 --> 00:04:51,360 Anion. That's where convention steps 99 00:04:51,360 --> 00:04:53,440 in. Since precise partitioning is 100 00:04:53,440 --> 00:04:56,240 impossible, we establish an arbitrary starting point. 101 00:04:56,720 --> 00:05:00,280 A widely adopted convention is to take the radius of the large 102 00:05:00,280 --> 00:05:04,440 rigid oxide ion O2 minus as 140 kilometers. 103 00:05:04,440 --> 00:05:05,960 So we just decide that's the number. 104 00:05:06,160 --> 00:05:10,200 We decide, and once that arbitrary value is fixed, we can 105 00:05:10,200 --> 00:05:12,080 determine the radius of other ions. 106 00:05:12,480 --> 00:05:15,960 For example, to find the radius of MG2 plus, you measure the 107 00:05:15,960 --> 00:05:19,520 bond length in Mgo and just subtract the conventional 1:40 108 00:05:19,520 --> 00:05:23,240 PM radius of the oxide ion. It is an empirical system, but 109 00:05:23,240 --> 00:05:25,920 it works. So synthesizing those 110 00:05:25,920 --> 00:05:29,640 measurements, the general trends hold true because of ZF and the 111 00:05:29,640 --> 00:05:31,360 quantum number N. Exactly. 112 00:05:31,600 --> 00:05:33,440 Atomic radii increase down a group. 113 00:05:33,440 --> 00:05:36,920 Because the principal quantum number N increases, you're 114 00:05:36,920 --> 00:05:39,280 adding new, larger electron shells. 115 00:05:39,360 --> 00:05:42,360 And they shrink across a period. They decrease from left to right 116 00:05:42,360 --> 00:05:45,720 across a period because the consistently increasing ZF pulls 117 00:05:45,720 --> 00:05:48,560 the valence shells tighter to the nucleus, overriding the 118 00:05:48,560 --> 00:05:51,560 minimal increase in size from electron electron repulsion. 119 00:05:51,640 --> 00:05:53,440 OK. Moving from physical size to 120 00:05:53,440 --> 00:05:56,840 chemical potential, we start with ionization energy, IY. 121 00:05:57,200 --> 00:06:00,040 This is the minimum energy required to strip an electron 122 00:06:00,040 --> 00:06:03,680 away from a gas phase atom. Right, the process a gas goes to 123 00:06:03,840 --> 00:06:08,200 a plus gas plus an electron. The first ionization energy I-1 124 00:06:08,200 --> 00:06:10,440 removes the least tightly bound electron. 125 00:06:10,440 --> 00:06:13,920 And then successive ones I2I3 they always get bigger. 126 00:06:14,080 --> 00:06:17,040 They increase progressively because you are trying to remove 127 00:06:17,040 --> 00:06:20,720 an electron from an increasingly positive ion, and the energy 128 00:06:20,720 --> 00:06:23,800 difference is particularly vast when you jump from removing a 129 00:06:23,800 --> 00:06:26,720 valence electron to removing a core electron. 130 00:06:27,080 --> 00:06:30,440 But the smooth trend across a period isn't perfectly smooth. 131 00:06:30,800 --> 00:06:34,080 We see these little drops. The drop from beryllium to boron 132 00:06:34,080 --> 00:06:36,880 is a classic example. That drop occurs because the 133 00:06:36,920 --> 00:06:40,880 outermost electron in boron occupies a 2P orbital, which is 134 00:06:40,880 --> 00:06:44,080 both slightly higher in energy and slightly shielded by the 2 135 00:06:44,080 --> 00:06:46,160 ^2 electrons. So it's just easier to pull off. 136 00:06:46,200 --> 00:06:49,360 It's less strongly bound than the Two's electron in beryllium, 137 00:06:49,360 --> 00:06:53,160 leading to a small but noticeable drop in I-1, and you 138 00:06:53,160 --> 00:06:56,240 see a similar dip from nitrogen to oxygen due to the 139 00:06:56,240 --> 00:06:59,000 destabilization you get from pairing up electrons in the 140 00:06:59,000 --> 00:07:02,120 corpitals. Next is electron affinity EA, 141 00:07:02,120 --> 00:07:04,400 which is related to the electron gain and dilapi. 142 00:07:04,680 --> 00:07:06,920 This is always a source of confusion because of the sign 143 00:07:06,920 --> 00:07:09,160 conventions. Can you clarify that for us? 144 00:07:09,480 --> 00:07:11,160 Absolutely. This trips up many students. 145 00:07:11,600 --> 00:07:14,680 Electron gain enthalpy is the energy change when an atom gains 146 00:07:14,680 --> 00:07:17,240 an electron. Since most atoms release energy 147 00:07:17,240 --> 00:07:20,160 when they do this, it's typically a negative exothermic 148 00:07:20,200 --> 00:07:21,240 value. OK. 149 00:07:21,360 --> 00:07:25,720 In contrast, electron affinity EA is often defined as the 150 00:07:25,760 --> 00:07:29,320 energy required to remove that added electron from the anion. 151 00:07:29,880 --> 00:07:32,280 So a positive EA means the anion is stable. 152 00:07:32,280 --> 00:07:33,960 You have to put energy in to break it apart. 153 00:07:33,960 --> 00:07:37,240 So if an atom has a high positive EA, it means the 154 00:07:37,240 --> 00:07:40,400 resulting anion is much more stable than the neutral atom, 155 00:07:40,600 --> 00:07:43,000 reflecting a strong drive to acquire that electron. 156 00:07:43,000 --> 00:07:44,880 Correct. And we observed that electron 157 00:07:44,880 --> 00:07:47,360 affinities are highest for elements near fluorine. 158 00:07:47,760 --> 00:07:50,200 Actually, chlorine has the highest because they have the 159 00:07:50,200 --> 00:07:52,280 strongest desire to complete their octave. 160 00:07:52,480 --> 00:07:56,400 These two energies feed directly into electronegativity, but this 161 00:07:56,400 --> 00:07:58,360 property is fundamentally different, isn't it? 162 00:07:58,760 --> 00:08:01,360 It is different because it is a contextual property. 163 00:08:01,640 --> 00:08:05,120 Electronegativity is the power of an atom to attract electrons 164 00:08:05,120 --> 00:08:07,720 when it is part of a compound or chemical bond. 165 00:08:08,040 --> 00:08:11,160 It's a measure of pulling strength within a bond, not the 166 00:08:11,160 --> 00:08:14,080 inherent stability of an isolated atom or ion. 167 00:08:14,080 --> 00:08:17,760 And like ionization energy, it increases across the period and 168 00:08:17,760 --> 00:08:20,560 decreases down to group. Right, for the same reasons ZF 169 00:08:20,560 --> 00:08:22,640 and atomic size. And since we can't measure 170 00:08:22,640 --> 00:08:25,600 directly, we have multiple scales trying to approximate 171 00:08:25,600 --> 00:08:28,280 this pole. Yes, reflecting its complexity, 172 00:08:28,800 --> 00:08:32,280 the Pauling scale is derived empirically from bond energies. 173 00:08:32,559 --> 00:08:35,080 The Molecan scale is more theoretical. 174 00:08:35,240 --> 00:08:39,159 It defines electronegativity as the average of ionization energy 175 00:08:39,159 --> 00:08:41,720 and electron affinity. So the tendency to lose an 176 00:08:41,720 --> 00:08:43,520 electron and the tendency to gain 1. 177 00:08:43,640 --> 00:08:46,040 Exactly. And then the Allred Rocha scale 178 00:08:46,040 --> 00:08:49,200 is based on classical physics. It defines electronegativity 179 00:08:49,200 --> 00:08:52,000 based on the electrostatic force, which is proportional to 180 00:08:52,000 --> 00:08:55,520 ZF over R-squared. All three are useful in their 181 00:08:55,520 --> 00:08:57,640 own way. Following electronegativity, we 182 00:08:57,640 --> 00:09:01,040 discussed polarizability. If electronegativity is the 183 00:09:01,040 --> 00:09:04,880 power to pull, polarizability is the power to to yield. 184 00:09:04,880 --> 00:09:07,400 Precisely. Polarizability is the ability of 185 00:09:07,400 --> 00:09:10,400 an atom's electron cloud to be distorted by an external 186 00:09:10,400 --> 00:09:12,400 electric field, like from a nearby ion. 187 00:09:12,720 --> 00:09:15,080 This ability is maximized in species that hold their 188 00:09:15,080 --> 00:09:17,840 electrons loosely. So big squishy onions. 189 00:09:17,960 --> 00:09:21,520 Big squishy onions with lots of diffuse electrons, low charge 190 00:09:21,520 --> 00:09:23,720 density, and low effective nuclear charge. 191 00:09:23,760 --> 00:09:25,400 They're easily distorted. OK. 192 00:09:25,880 --> 00:09:29,320 Low ionization energy translates directly to metallic character, 193 00:09:29,360 --> 00:09:32,880 the ease of losing electrons. This leads us to oxidation 194 00:09:32,880 --> 00:09:36,080 states for main group elements. They generally follow 195 00:09:36,080 --> 00:09:39,600 predictable rules, but the heavier P block elements behave 196 00:09:39,600 --> 00:09:42,040 weirdly due to the inert pair effect. 197 00:09:42,080 --> 00:09:45,240 The inert pair effect is a major deviation in the heavier 198 00:09:45,240 --> 00:09:48,760 elements of groups 1314 and 15. Like thallium, lead, and 199 00:09:48,760 --> 00:09:51,480 bismuth. The most stable oxidation state 200 00:09:51,560 --> 00:09:54,280 often becomes 2 units lower than the group valence. 201 00:09:54,280 --> 00:09:56,480 So plus one instead +3 for thallium. 202 00:09:56,560 --> 00:10:00,160 Exactly this is because the pair of n ^2 electrons becomes 203 00:10:00,160 --> 00:10:02,760 progressively reluctant to participate in bonding. 204 00:10:02,760 --> 00:10:06,040 They become inert. Why are those n ^2 electrons 205 00:10:06,040 --> 00:10:08,920 suddenly so inert compared to the NP electrons? 206 00:10:08,920 --> 00:10:11,960 It's a combination of pore shielding and something more 207 00:10:11,960 --> 00:10:13,920 fundamental relativistic effects. 208 00:10:14,120 --> 00:10:17,480 As Z gets really large, the innermost electrons move at 209 00:10:17,480 --> 00:10:19,200 speeds approaching the speed of light. 210 00:10:19,760 --> 00:10:22,880 Relativistic mechanics dictates that their mass increases, which 211 00:10:22,880 --> 00:10:26,200 causes their orbits to contract. This contraction pulls the end 212 00:10:26,200 --> 00:10:29,160 as orbital in, makes it lower in energy and much less available 213 00:10:29,160 --> 00:10:32,400 for bonding, so it's easier to just lose the NP electrons. 214 00:10:32,560 --> 00:10:35,640 That's a wonderful example of how fundamental physics effects 215 00:10:35,640 --> 00:10:38,520 chemical stability. Now what about the D block 216 00:10:38,520 --> 00:10:40,880 states? They show much more variety. 217 00:10:41,040 --> 00:10:44,400 D Block elements, particularly up to manganese, can exhibit a 218 00:10:44,400 --> 00:10:47,560 maximum oxidation state equal to their group number, like 219 00:10:47,560 --> 00:10:50,840 manganese 7 plus. But these high states are only 220 00:10:50,840 --> 00:10:54,440 reached when stabilized by highly electronegative elements, 221 00:10:54,840 --> 00:10:57,560 and it's critical to know that oxygen is much better at this 222 00:10:57,560 --> 00:11:00,120 than fluorine. Why is oxygen superior to 223 00:11:00,120 --> 00:11:01,480 fluorine? Here fluorine is the most 224 00:11:01,480 --> 00:11:04,520 electronegative element. Fluorine can only form a single 225 00:11:04,520 --> 00:11:06,920 bond. If you need to balance a + 7 226 00:11:06,920 --> 00:11:10,360 charge on manganese, you would need 7 fluoride ions, which 227 00:11:10,360 --> 00:11:12,280 creates immense stearic crowding. 228 00:11:12,280 --> 00:11:16,040 Just too many atoms to fit. Oxygen, however, can form double 229 00:11:16,040 --> 00:11:19,480 bonds or act as a bridging oxide, so you need far fewer 230 00:11:19,480 --> 00:11:22,000 oxygen atoms. Only four are required in the 231 00:11:22,000 --> 00:11:25,720 permanganate ion to stabilize that high charge, minimizing 232 00:11:25,720 --> 00:11:27,840 stearic hindrance. OK, anomalies. 233 00:11:28,040 --> 00:11:31,280 The first member of each group. Carbon, for instance, is often 234 00:11:31,280 --> 00:11:33,560 an odd duck. Their behavior is anomalous for 235 00:11:33,560 --> 00:11:37,800 two reasons, a small atomic radius and the crucial lack of 236 00:11:37,800 --> 00:11:40,760 accessible D orbitals. Without D orbitals, they are 237 00:11:40,760 --> 00:11:43,400 limited to a maximum coordination number of four. 238 00:11:43,720 --> 00:11:45,400 And this leads to unique bonding. 239 00:11:45,400 --> 00:11:47,800 It does. Carbon, for instance, forms 240 00:11:47,800 --> 00:11:51,280 extremely strong pie bonds, allowing for double and triple 241 00:11:51,280 --> 00:11:54,400 bonds. Silicon, its bigger cousin, has 242 00:11:54,400 --> 00:11:57,960 poor poor orbital overlap and prefers to form single bonds in 243 00:11:57,960 --> 00:12:01,400 these big network structures. The small size also leads to the 244 00:12:01,400 --> 00:12:03,240 diagonal relationships we often see. 245 00:12:03,320 --> 00:12:06,200 Right elements diagonally opposed, like lithium and 246 00:12:06,200 --> 00:12:09,680 magnesium or beryllium and aluminum show similarities 247 00:12:09,680 --> 00:12:13,080 because the decrease in size across a period is almost 248 00:12:13,080 --> 00:12:15,960 exactly compensated by the increase in size down a group. 249 00:12:16,040 --> 00:12:19,000 So they end up with similar charge to radius ratios and 250 00:12:19,000 --> 00:12:21,400 electronegativities. And therefore very similar 251 00:12:21,400 --> 00:12:23,720 chemistry. Let's link this atomic behavior 252 00:12:23,720 --> 00:12:27,200 to bulk stability using bond enthalpy trends measured as the 253 00:12:27,240 --> 00:12:30,120 enthalpy of atomization. Across a period, this value 254 00:12:30,120 --> 00:12:33,320 generally increases, peaking dramatically at Group 14 with 255 00:12:33,320 --> 00:12:36,080 carbon and silicon. Because of those strong 256 00:12:36,080 --> 00:12:38,320 extensive network covalent structures. 257 00:12:38,680 --> 00:12:41,160 Exactly. Diamond and silicon are 258 00:12:41,160 --> 00:12:44,080 incredibly hard, high melting point solids. 259 00:12:44,520 --> 00:12:47,720 Then the value drops off a Cliff as we get to molecular elements 260 00:12:47,720 --> 00:12:51,720 like nitrogen and oxygen, which are held together by much weaker 261 00:12:51,720 --> 00:12:54,520 intermolecular forces. And the change down a group 262 00:12:54,520 --> 00:12:57,440 reveals a major dichotomy between this block and the D 263 00:12:57,440 --> 00:12:59,600 block. This is a critical distinction 264 00:12:59,760 --> 00:13:03,640 for S&P block elements. Bond strength decreases down a 265 00:13:03,640 --> 00:13:05,480 group. The P orbitals become 266 00:13:05,480 --> 00:13:09,400 increasingly diffuse, leading to poor orbital overlap and weaker 267 00:13:09,400 --> 00:13:10,960 bonds. But for the D block. 268 00:13:11,040 --> 00:13:13,680 The opposite occurs. Bond strength increases down a 269 00:13:13,680 --> 00:13:17,080 group from 3rd into 5 pent. This is because the D orbitals 270 00:13:17,080 --> 00:13:20,040 in the lighter 3 battles are highly contracted and actually 271 00:13:20,040 --> 00:13:22,400 pretty poor at overlaps. So they're not the right size 272 00:13:22,400 --> 00:13:23,400 yet. Not really. 273 00:13:23,520 --> 00:13:26,480 As you move to the four and five pent series, the D orbitals 274 00:13:26,480 --> 00:13:28,960 expand to become optimally sized for overlap. 275 00:13:29,240 --> 00:13:32,000 This results in 5 bent metals having dramatically higher 276 00:13:32,000 --> 00:13:34,840 atomization enthalpies, which contributes to their high 277 00:13:34,840 --> 00:13:36,840 melting points and stability. That. 278 00:13:36,840 --> 00:13:39,760 Deep structural difference is a perfect bridge to our next 279 00:13:39,760 --> 00:13:42,080 module. Let's take these fundamental 280 00:13:42,080 --> 00:13:44,920 properties and apply them to predict how compounds react, 281 00:13:45,120 --> 00:13:48,240 focusing on acids, bases and redox potentials. 282 00:13:49,040 --> 00:13:52,840 So Brenstad acids. In water we see these classes 283 00:13:53,240 --> 00:13:55,960 Aqua acids, hydroxyl acids and Oxo acids. 284 00:13:56,040 --> 00:13:59,440 Right, and they often represent successive deprotonation stages 285 00:13:59,440 --> 00:14:03,400 of a highly charged metal ion coordinated to water molecules. 286 00:14:03,480 --> 00:14:06,880 The largest and most predictable class is the Oxo acids, where 287 00:14:06,880 --> 00:14:09,680 the strength is elegantly summarized by Pauling's rules. 288 00:14:10,200 --> 00:14:12,880 Pauling noted that the strength of an Oxo acid increases with 289 00:14:12,880 --> 00:14:15,080 the number of non protonated oxygen atoms. 290 00:14:15,440 --> 00:14:20,880 So perchloric acid HCLO 4 with three non protonated oxygens is 291 00:14:20,880 --> 00:14:24,760 way stronger than hypochlorous acid HCLO which has none. 292 00:14:25,080 --> 00:14:28,000 Pauling's rules feel like a wonderful shortcut, but what's 293 00:14:28,000 --> 00:14:30,360 the physical mechanism? Why is it specifically the 294 00:14:30,360 --> 00:14:32,120 number of non protonated oxygens? 295 00:14:32,280 --> 00:14:34,120 It's purely an electronic effect. 296 00:14:34,120 --> 00:14:37,400 The non protonated oxygen atoms are extremely electronegative. 297 00:14:37,600 --> 00:14:40,480 They act as powerful electron withdrawing groups, pulling 298 00:14:40,480 --> 00:14:42,560 electron density away from the central atom. 299 00:14:42,720 --> 00:14:44,720 And that pole cascades through the molecule. 300 00:14:44,840 --> 00:14:47,360 It does. It pulls density away from the 301 00:14:47,360 --> 00:14:50,760 OH bond, which polarizes and weakens it, making the proton 302 00:14:50,760 --> 00:14:53,760 much easier to release. And on top of that, once the 303 00:14:53,760 --> 00:14:56,960 proton leaves the negative charge on, the resulting anion 304 00:14:56,960 --> 00:14:59,680 is delocalized over all those extra oxygens. 305 00:14:59,680 --> 00:15:01,560 Which stabilizes the conjugate base. 306 00:15:01,560 --> 00:15:04,440 Exactly. A more stable conjugate base 307 00:15:04,440 --> 00:15:08,680 means a stronger original acid. This metal versus nonmetal 308 00:15:08,680 --> 00:15:11,240 character also defines the nature of oxides. 309 00:15:11,400 --> 00:15:14,160 Generally, yes. Metal oxides are basic, Nonmetal 310 00:15:14,160 --> 00:15:16,480 oxides are acidic, and the transition zone involves 311 00:15:16,480 --> 00:15:20,240 ampiteric oxides, which can react with both acids and bases. 312 00:15:20,240 --> 00:15:22,640 Like aluminum oxide? Aluminum oxide is the classic 313 00:15:22,800 --> 00:15:24,720 example. You find these on the metal non 314 00:15:24,720 --> 00:15:27,600 metal frontier. Amphoturism is intrinsically 315 00:15:27,600 --> 00:15:30,720 linked to having a significant degree of covalent character in 316 00:15:30,720 --> 00:15:33,600 the metal oxygen bond. It's not fully ionic, not fully 317 00:15:33,600 --> 00:15:35,640 covalent, so it can play both sides OK. 318 00:15:35,800 --> 00:15:39,520 Shifting to electron pair donors and acceptors, Lewis Chemistry 319 00:15:39,880 --> 00:15:43,760 Group 13 elements, specifically boron trihalides, are the poster 320 00:15:43,760 --> 00:15:45,720 children for Lewis acids. They are. 321 00:15:45,800 --> 00:15:49,400 They're classic electron pair acceptors utilizing a vacant P 322 00:15:49,400 --> 00:15:53,200 orbital, but the trend of acidity is counterintuitive. 323 00:15:53,560 --> 00:15:56,880 Boron trifluoride is a weaker Lewis acid than boron 324 00:15:56,880 --> 00:16:00,360 trichloride or boron tribromide. Which seems backwards since 325 00:16:00,360 --> 00:16:02,480 fluorine is so electronegative. It does. 326 00:16:02,800 --> 00:16:05,440 The phenomenon is explained by back bonding. 327 00:16:05,920 --> 00:16:10,000 The small fluorine atoms filled P orbitals are the right size to 328 00:16:10,000 --> 00:16:13,160 donate some electron density back into boron's empty P 329 00:16:13,160 --> 00:16:16,160 orbital, which slightly alleviates boron's electron 330 00:16:16,160 --> 00:16:18,320 deficiency. And the bigger chlorine and 331 00:16:18,320 --> 00:16:20,120 bromine atoms can't do that as well. 332 00:16:20,160 --> 00:16:22,960 They're P orbitals are too large and diffuse for effective 333 00:16:22,960 --> 00:16:27,120 overlap, leaving BCL 3 and BBR 3 more electron hungry and thus 334 00:16:27,120 --> 00:16:30,360 stronger Lewis acids. And we saw how important this is 335 00:16:30,360 --> 00:16:32,960 in biological systems, specifically with carbon 336 00:16:32,960 --> 00:16:36,600 monoxide toxicity. CEO is a fantastic Lewis base. 337 00:16:36,800 --> 00:16:39,640 It's affinity for the Iron 2 center and hemoglobin is much, 338 00:16:39,640 --> 00:16:43,360 much higher than that of oxygen. Once the CEO forms that stable 339 00:16:43,360 --> 00:16:45,720 coordinate bond, it is almost irreversible. 340 00:16:45,720 --> 00:16:48,240 It just doesn't let go. Which effectively starves the 341 00:16:48,240 --> 00:16:50,040 body of oxygen. Exactly. 342 00:16:50,520 --> 00:16:53,000 It highlights how minute differences in Lewis specificity 343 00:16:53,000 --> 00:16:56,000 can have fatal consequences. Here's where we get predictive 344 00:16:56,920 --> 00:17:00,400 the hard soft acid base or HS A/B concept. 345 00:17:00,560 --> 00:17:03,040 HS A/B simplifies stability prediction. 346 00:17:03,240 --> 00:17:06,599 Hard species are small, highly charged and non polarizable. 347 00:17:06,599 --> 00:17:09,599 Think H plus aluminum 3 plus fluoride. 348 00:17:09,720 --> 00:17:12,680 They favor electrostatic ionic interactions. 349 00:17:12,680 --> 00:17:15,200 In saw species. Soft species are large, have low 350 00:17:15,200 --> 00:17:17,560 charge density, and are highly polarizable. 351 00:17:17,720 --> 00:17:21,800 Their electron clouds are mushy. Think Mercury 2 plus iodide 352 00:17:21,800 --> 00:17:24,359 sulfide. They favor covalent overlap. 353 00:17:24,480 --> 00:17:28,200 And the fundamental rule is hard acids prefer hard bases and soft 354 00:17:28,200 --> 00:17:30,280 acids prefer soft bases. That's it. 355 00:17:30,560 --> 00:17:32,920 We see this empirically in halide stability. 356 00:17:33,240 --> 00:17:36,520 A hard acid like aluminum 3 plus forms its most stable complex 357 00:17:36,520 --> 00:17:39,840 with the hardest base fluoride. A soft acid like mercury 2 plus 358 00:17:39,840 --> 00:17:42,000 does the opposite. It prefers the softest base 359 00:17:42,000 --> 00:17:44,400 iodide. HSAB feels inherently 360 00:17:44,400 --> 00:17:46,440 qualitative. Yeah, we try to quantify it 361 00:17:46,440 --> 00:17:49,440 using the Dragawaylen model. How accurately does a simple 362 00:17:49,440 --> 00:17:51,400 equation like that capture the complexity? 363 00:17:51,520 --> 00:17:55,040 It captures it remarkably well, primarily because the E&C 364 00:17:55,040 --> 00:17:57,600 parameters are empirical. They're fit to experimental 365 00:17:57,600 --> 00:18:00,440 data, but the model is based on the idea that the total 366 00:18:00,440 --> 00:18:03,280 interaction energy can be successfully broken into two 367 00:18:03,280 --> 00:18:05,640 separate contributions. The electrostatic and the 368 00:18:05,640 --> 00:18:08,240 covalent parts. Right E represents the 369 00:18:08,240 --> 00:18:12,200 electrostatic or hard component. C represents the propensity for 370 00:18:12,200 --> 00:18:15,320 covalent bonding the soft component, and by fitting these 371 00:18:15,320 --> 00:18:17,960 parameters, the model successfully predicts reaction 372 00:18:17,960 --> 00:18:21,320 enthalpies for a huge variety of acid base reactions. 373 00:18:21,320 --> 00:18:23,760 And linking this back to the entire planet, we have the 374 00:18:23,760 --> 00:18:27,640 Goldschmidt classification showing that HSAB dictates where 375 00:18:27,640 --> 00:18:30,480 elements are found on Earth. That's one of the most powerful 376 00:18:30,480 --> 00:18:34,360 applications lithophiles. Rock lovers are hard acids like 377 00:18:34,360 --> 00:18:38,800 sodium, magnesium, aluminum. They bind to the hard base oxide 378 00:18:38,800 --> 00:18:41,280 and are concentrated in the Earth's silicate crust. 379 00:18:41,320 --> 00:18:43,120 And chalcophiles. Chalcophiles. 380 00:18:43,120 --> 00:18:47,040 Sulfide levers are soft assets like cadmium, lead, bismuth. 381 00:18:47,320 --> 00:18:50,360 They bind to the soft base sulphide and are found deep in 382 00:18:50,360 --> 00:18:53,480 sulphide ore deposits. It's a unifying concept that 383 00:18:53,480 --> 00:18:56,240 connects electron density right to geology. 384 00:18:56,440 --> 00:18:59,520 OK. If HSAB predicts stability based 385 00:18:59,520 --> 00:19:03,200 on orbital overlap, then redox chemistry predicts stability 386 00:19:03,200 --> 00:19:06,680 based on electron transfer. We use standard reduction 387 00:19:06,680 --> 00:19:09,680 potentials measured against the standard hydrogen electrode. 388 00:19:09,680 --> 00:19:12,880 Which is set to 0 volts. Yeah, a spontaneous cell 389 00:19:12,880 --> 00:19:16,200 reaction requires the overall cell potential to be positive. 390 00:19:16,440 --> 00:19:19,720 The electrochemical series just ranks half reactions by their 391 00:19:19,720 --> 00:19:21,840 potential. High positive potential means 392 00:19:21,840 --> 00:19:25,640 it's a strong oxidizing agent. Easily reduced, yes, like 393 00:19:25,640 --> 00:19:28,880 fluorine bass, a low negative potential means it's easily 394 00:19:28,880 --> 00:19:31,280 oxidized. A strong reducing agent like 395 00:19:31,280 --> 00:19:33,480 lithium metal. We use this to predict 396 00:19:33,480 --> 00:19:37,640 thermodynamic stability, particularly whether a species 397 00:19:37,640 --> 00:19:40,360 will spontaneously react with itself, which is 398 00:19:40,360 --> 00:19:43,320 disproportionation. Disproportionation occurs when a 399 00:19:43,320 --> 00:19:46,360 species in an intermediate oxidation state converts into 400 00:19:46,360 --> 00:19:48,720 both a higher and a lower oxidation state. 401 00:19:49,000 --> 00:19:52,080 For it to be spontaneous, the potential for its reduction step 402 00:19:52,080 --> 00:19:54,880 must be greater than the potential for its oxidation 403 00:19:54,880 --> 00:19:56,160 step. And as we've said, the 404 00:19:56,160 --> 00:19:58,520 environment matters. Complexation effects can 405 00:19:58,520 --> 00:20:01,200 dramatically stabilize specific oxidation states. 406 00:20:01,400 --> 00:20:04,200 Ligands are essential ligers in redox control. 407 00:20:04,760 --> 00:20:08,200 If a ligand binds much more strongly to the oxidized form of 408 00:20:08,200 --> 00:20:11,360 a metal than the reduced form, it makes the reduction process 409 00:20:11,360 --> 00:20:14,320 harder, more negative. It shifts the potential. 410 00:20:14,360 --> 00:20:17,720 Which is how we design complexes for specific catalytic or 411 00:20:17,720 --> 00:20:19,400 biological roles. Absolutely. 412 00:20:19,600 --> 00:20:23,120 You can tune the redox potential by volts just by changing the 413 00:20:23,120 --> 00:20:25,240 ligands. Now for the graphical summaries 414 00:20:25,240 --> 00:20:27,720 of deduct stability. Let's start with Latimer 415 00:20:27,720 --> 00:20:30,440 diagrams. They are quantitative, but often 416 00:20:30,440 --> 00:20:32,640 lead to calculation errors. They do. 417 00:20:32,920 --> 00:20:36,760 A Latimer diagram summarizes adjacent oxidation States and 418 00:20:36,760 --> 00:20:39,680 the potential between them. The trap is calculating the 419 00:20:39,680 --> 00:20:41,800 potential for non adjacent species. 420 00:20:42,080 --> 00:20:43,920 You cannot simply add the potentials. 421 00:20:43,920 --> 00:20:45,840 Because potential isn't an extensive. 422 00:20:45,840 --> 00:20:48,040 Property right? You must first use the 423 00:20:48,040 --> 00:20:52,760 relationship delta G equals minus nu Fe to convert each 424 00:20:52,760 --> 00:20:55,760 potential into Gibbs free energy, which is extensive. 425 00:20:56,080 --> 00:20:58,920 You sum the Gibbs energies and then you convert back to a 426 00:20:58,920 --> 00:21:00,880 potential. That is the most common mistake 427 00:21:00,920 --> 00:21:02,800 every time. Then we have the frost diagram, 428 00:21:02,920 --> 00:21:05,200 which gives us a much more intuitive visual summary. 429 00:21:05,360 --> 00:21:09,040 The frost diagram plots a value proportional to Gibbs energy 430 00:21:09,040 --> 00:21:13,160 versus the oxidation number, and this provides 4 rapid visual 431 00:21:13,160 --> 00:21:14,200 insights. OK, what are they? 432 00:21:14,360 --> 00:21:17,360 First, stability? The species at the lowest point 433 00:21:17,360 --> 00:21:20,880 on the plot is the most thermodynamically stable second 434 00:21:21,000 --> 00:21:23,760 driving force. The slow of the line connecting 435 00:21:23,760 --> 00:21:26,400 any 2 secies gives the reduction potential. 436 00:21:26,600 --> 00:21:29,760 A steep positive slope means it's a favorable reduction. 437 00:21:29,760 --> 00:21:34,640 And 3rd. 3rd disproportionation. If a species sits at a point 438 00:21:34,640 --> 00:21:38,160 above the line connecting its two neighbors, a convex curve, 439 00:21:38,440 --> 00:21:41,560 it's unstable and will spontaneously disproportionate. 440 00:21:41,560 --> 00:21:43,360 And the opposite is comproportionation. 441 00:21:43,400 --> 00:21:45,400 Right. If a species lies below the 442 00:21:45,400 --> 00:21:49,160 line, a concave curve is highly stable and will be formed by its 443 00:21:49,160 --> 00:21:52,000 neighbors reacting together. That graphical interpretation 444 00:21:52,000 --> 00:21:55,320 provides an immediate check on stability, but we know chemical 445 00:21:55,320 --> 00:21:59,240 stability depends heavily on pH. That brings us to the pourbait 446 00:21:59,240 --> 00:22:02,200 diagram. Pourbait diagram, or Eph diagram 447 00:22:02,400 --> 00:22:06,240 maps the thermodynamic stability fields of species in water as a 448 00:22:06,240 --> 00:22:08,120 function of both potential and pH. 449 00:22:08,520 --> 00:22:11,040 It's the cornerstone of corrosion and environmental 450 00:22:11,040 --> 00:22:12,560 chemistry. And the boundaries are key. 451 00:22:12,840 --> 00:22:14,760 The boundaries tell you the type of reaction. 452 00:22:15,200 --> 00:22:17,560 Vertical boundaries are proton transfer only. 453 00:22:17,680 --> 00:22:20,720 Horizontal boundaries are electron transfer only, and 454 00:22:20,720 --> 00:22:23,840 sloped boundaries involve both. The classic example is the 455 00:22:23,840 --> 00:22:26,080 stability of iron 3 plus in water. 456 00:22:26,360 --> 00:22:28,440 Right. If you look at the Faipor Bay 457 00:22:28,440 --> 00:22:32,640 diagram, the stable field for the soluble iron 3 plus ion is 458 00:22:32,640 --> 00:22:36,480 restricted to very acidic, highly oxidizing conditions. 459 00:22:37,120 --> 00:22:40,360 As the pH approaches neutral, the stability field shifts 460 00:22:40,360 --> 00:22:43,680 entirely toward insoluble iron 3 hydroxide. 461 00:22:43,680 --> 00:22:47,200 Which is why there's almost no soluble iron in natural waters. 462 00:22:47,560 --> 00:22:49,280 Unless they're highly acidic. Exactly. 463 00:22:49,280 --> 00:22:52,520 It precipitates out as rust. Finally, we use thermodynamics 464 00:22:52,520 --> 00:22:55,560 in industry via the Ellingham diagram for metal extraction. 465 00:22:56,040 --> 00:22:58,720 Ellingham diagrams plot the Gibbs energy of formation of 466 00:22:58,720 --> 00:23:02,120 metal oxides versus temperature. Since forming a metal oxide 467 00:23:02,120 --> 00:23:05,440 consumes oxygen gas, the entropy change is highly negative, so 468 00:23:05,440 --> 00:23:07,640 the slopes of the lines are almost always positive. 469 00:23:07,640 --> 00:23:11,880 And reduction is possible when. To reduce a metal oxide using, 470 00:23:11,880 --> 00:23:15,680 say, carbon, the reaction becomes spontaneous when the 471 00:23:15,680 --> 00:23:17,480 overall Gibbs energy is negative. 472 00:23:18,120 --> 00:23:20,680 This happens at the temperature where the line for the oxidation 473 00:23:20,680 --> 00:23:23,480 of carbon drops below the line for the formation of the metal 474 00:23:23,480 --> 00:23:26,120 oxide. So for zinc oxide, the crossover 475 00:23:26,120 --> 00:23:29,040 with the carbon line is around 1200° C. 476 00:23:29,200 --> 00:23:32,560 It is, and if we wanted to reduce magnesium oxide, which 477 00:23:32,560 --> 00:23:35,560 sits much lower on the diagram, the crossover doesn't happen 478 00:23:35,560 --> 00:23:39,560 until about 2100° C. And that difference is a direct 479 00:23:39,560 --> 00:23:42,400 consequence of the metals inherent atomic properties. 480 00:23:42,400 --> 00:23:46,040 Linking us right back to ZF and ionization energy from module 1. 481 00:23:46,160 --> 00:23:48,840 A perfect transition. Now let's leave aqueous 482 00:23:48,840 --> 00:23:52,320 solutions and move to the third pillar, the architecture and 483 00:23:52,320 --> 00:23:54,440 electronic properties of bulk solids. 484 00:23:54,440 --> 00:23:57,920 OK, when analyzing solids, we start by modeling atoms as hard 485 00:23:57,920 --> 00:23:59,320 spheres and seeing how they pack. 486 00:23:59,400 --> 00:24:01,080 Right. And the most efficient ways are 487 00:24:01,080 --> 00:24:04,400 the close packed structures. Hexagonal close packed HTP and 488 00:24:04,400 --> 00:24:08,520 cubic close packed CCP both achieved 74% volume occupancy. 489 00:24:08,680 --> 00:24:13,200 And the other 26% is empty space the holes. 490 00:24:13,280 --> 00:24:16,760 The voids are holes, yes. For crystal made of N spheres, 491 00:24:16,760 --> 00:24:20,320 we generate N octahedral holes and 2 N tetrahedral holes. 492 00:24:21,040 --> 00:24:24,760 These are essential because in ionic solids, the smaller 493 00:24:24,760 --> 00:24:28,240 cations occupy these voids formed by the larger anions. 494 00:24:28,240 --> 00:24:30,880 The size of the hole dictates which ions can fit. 495 00:24:30,880 --> 00:24:32,800 Correct. We use the radius ratio to 496 00:24:32,800 --> 00:24:35,120 predict this. For the larger octahedral holes, 497 00:24:35,120 --> 00:24:38,520 the limit is 0.414. For the smaller tetrahedral 498 00:24:38,520 --> 00:24:41,960 holes, it's .225. If the cation is too small, it 499 00:24:41,960 --> 00:24:44,240 rattles. If it's too large, it forces the 500 00:24:44,240 --> 00:24:46,840 lattice to expand. OK, using these principles we 501 00:24:46,840 --> 00:24:48,760 can define the characteristic ionic structures. 502 00:24:48,760 --> 00:24:52,400 Give us a few key examples. The rock salt structure and ACL. 503 00:24:52,440 --> 00:24:55,880 The chlorine anions form a CCP array and the sodium cations 504 00:24:55,880 --> 00:24:59,560 occupy all the octahedral holes. The Rutel structure TIO 2. 505 00:25:00,000 --> 00:25:03,080 Here the cations occupy only half of the octahedral holes and 506 00:25:03,080 --> 00:25:07,640 the fluorite structure CKF of 2. The cations form a CCP array and 507 00:25:07,640 --> 00:25:10,160 the smaller fluoride anions occupy all the tetrahedral 508 00:25:10,160 --> 00:25:12,360 holes. And the more complex 3 component 509 00:25:12,360 --> 00:25:14,320 structures are essential for modern materials. 510 00:25:14,600 --> 00:25:16,520 The perovskite structure is a prime example. 511 00:25:16,640 --> 00:25:19,960 The perovskite structure ABO 3 is highly versatile. 512 00:25:20,280 --> 00:25:24,360 You can visualize it as a CCP array of the air cations and the 513 00:25:24,400 --> 00:25:27,960 oxide anions, with the B cations filling the octahedral holes 514 00:25:27,960 --> 00:25:31,440 formed by the oxygen network. The spinel structure AB2O four 515 00:25:31,440 --> 00:25:34,200 is important because it dictates how two different cations 516 00:25:34,200 --> 00:25:37,040 distribute themselves. Right, in a normal spinel, the A 517 00:25:37,160 --> 00:25:40,000 cation is in the tetrahedral holes and the B cation is in the 518 00:25:40,000 --> 00:25:42,680 octahedral holes. But the crucial variant is the 519 00:25:42,680 --> 00:25:45,600 inverse spinal. Here the aocation and half of 520 00:25:45,600 --> 00:25:49,280 the B cations switch locations. So the B cations are now in some 521 00:25:49,280 --> 00:25:51,960 of the tetrautral sites. Yes, and the aocation and the 522 00:25:51,960 --> 00:25:54,480 remaining B cations share the octahedral sites. 523 00:25:54,920 --> 00:25:57,920 Magnetite F3O4IS the most famous example. 524 00:25:58,200 --> 00:26:00,600 The magnetic properties depend critically on this site 525 00:26:00,600 --> 00:26:03,000 distribution. Finally, we have the extremes of 526 00:26:03,000 --> 00:26:05,880 covalent network solids like diamond and graphite. 527 00:26:06,080 --> 00:26:09,400 Diamond, where every carbon is P3 hybridized and bonded 528 00:26:09,400 --> 00:26:12,840 tetrahedrally, results in a highly rigid 3 dimensional 529 00:26:12,840 --> 00:26:14,600 network. It's the hardest material known. 530 00:26:14,600 --> 00:26:17,960 Where's Graphite? Graphite is SP2 hybridized, 531 00:26:18,120 --> 00:26:20,920 forming strong planar layers held together by weak 532 00:26:20,920 --> 00:26:22,920 intermolecular van der Waals forces. 533 00:26:23,360 --> 00:26:27,040 This weak interaction allows the layers to slide, making graphite 534 00:26:27,040 --> 00:26:29,200 soft and electrically conductive. 535 00:26:29,520 --> 00:26:33,640 OK, to quantify the stability of these ionic solids, we return to 536 00:26:33,640 --> 00:26:36,120 thermodynamics and the Born Haber cycle. 537 00:26:36,240 --> 00:26:38,640 Right, which is an application of Hess's law. 538 00:26:39,120 --> 00:26:41,760 We use it to calculate the lattice enthalpy, which we can't 539 00:26:41,760 --> 00:26:45,280 measure directly by summing up all the other measurable steps. 540 00:26:45,280 --> 00:26:48,800 In a closed loop, the total energy change has to be 0. 541 00:26:49,120 --> 00:26:51,960 We can also try to calculate it theoretically using the Born 542 00:26:51,960 --> 00:26:55,880 Meyer equation, which relies heavily on a parameter unique to 543 00:26:55,880 --> 00:26:58,640 the crystal geometry. That parameter is the Matalon 544 00:26:58,640 --> 00:27:01,360 constant A. The equation balances the 545 00:27:01,360 --> 00:27:04,440 attractive electrostatic term with the short range repulsive 546 00:27:04,440 --> 00:27:07,680 term, and the Matalon constant is the geometric factor that 547 00:27:07,680 --> 00:27:10,880 sums up every single ions electrostatic interaction with 548 00:27:11,000 --> 00:27:13,160 every other ion in the entire lattice. 549 00:27:13,160 --> 00:27:15,440 It's all about the. Geometry inseparable from it. 550 00:27:15,680 --> 00:27:18,480 OK, we spend so much time modeling the perfect crystal, 551 00:27:19,240 --> 00:27:22,840 but the course teaches us that all real solids contain defects, 552 00:27:23,240 --> 00:27:25,880 and these imperfections are actually thermodynamically 553 00:27:25,880 --> 00:27:28,720 favorable. How can a defect which costs 554 00:27:28,720 --> 00:27:31,840 energy to form be favored? You've hit the core paradox. 555 00:27:32,120 --> 00:27:35,000 The formation of a point defect is always endothermic. 556 00:27:35,160 --> 00:27:37,560 It cost energy. Delta H is positive. 557 00:27:38,080 --> 00:27:41,480 However, the introduction of a defect creates a huge amount of 558 00:27:41,480 --> 00:27:44,080 positional disorder which dramatically increases the 559 00:27:44,080 --> 00:27:46,760 entropy of the system. So delta S is large and 560 00:27:46,760 --> 00:27:48,640 positive. Very and at any temperature 561 00:27:48,640 --> 00:27:53,000 above absolute 0, the Gibbs energy G = H minus TS controls 562 00:27:53,000 --> 00:27:55,880 spontaneity. Because that T delta S term is 563 00:27:55,880 --> 00:27:59,280 large and positive, the overall free energy change for defect 564 00:27:59,280 --> 00:28:01,680 formation becomes negative. So the imperfect crystal is 565 00:28:01,680 --> 00:28:04,280 actually more stable. It is the equilibrium structure. 566 00:28:04,320 --> 00:28:05,800 It's stabilized by its own entropy. 567 00:28:05,920 --> 00:28:08,280 What are the 2 main types of intrinsic point defects? 568 00:28:08,480 --> 00:28:11,760 We have shot key defects which are just vacancies, missing 569 00:28:11,760 --> 00:28:15,600 atoms or ions that occur in stowy rheometric ratios to 570 00:28:15,600 --> 00:28:18,680 maintain charge balance, and then there are Frenkel defects 571 00:28:18,680 --> 00:28:21,800 where an ion moves from its normal lattice site into an 572 00:28:21,800 --> 00:28:23,920 interstitial site leaving behind a vacancy. 573 00:28:23,920 --> 00:28:26,280 So vacancy interstitial pair. Exactly. 574 00:28:26,280 --> 00:28:28,160 More common in more open structures. 575 00:28:28,160 --> 00:28:32,320 Finally, we discussed non Stow ecumetric compounds like iron 1 576 00:28:32,320 --> 00:28:35,280 -, X oxide where the composition isn't fixed. 577 00:28:35,960 --> 00:28:38,040 What defines this class of materials? 578 00:28:38,200 --> 00:28:41,480 Non stoichiometric compounds deviate from the simple whole 579 00:28:41,480 --> 00:28:44,160 number ratios but retain the same fundamental crystal 580 00:28:44,160 --> 00:28:46,240 structure. This requires that the element 581 00:28:46,240 --> 00:28:49,680 involved possesses multiple accessible oxidation states to 582 00:28:49,680 --> 00:28:53,240 maintain electrical neutrality. So in that iron oxide some of 583 00:28:53,240 --> 00:28:55,080 the iron 2 plus ions are missing. 584 00:28:55,240 --> 00:28:58,320 Right, leaving competition vacancies and charge balance is 585 00:28:58,320 --> 00:29:02,640 maintained because 2 iron 2 plus ions are replaced by 1 iron 3 586 00:29:02,640 --> 00:29:05,800 plus for every vacancy created. That's why it's so common for 587 00:29:05,800 --> 00:29:08,760 D&F block elements. Understanding defects is the 588 00:29:08,760 --> 00:29:12,200 bridge to electronic structure. We move beyond molecular 589 00:29:12,200 --> 00:29:14,480 orbitals to band theory for bulk solids. 590 00:29:14,640 --> 00:29:18,000 Band theory extends the MO concept by treating the massive 591 00:29:18,000 --> 00:29:22,960 overlap of anatomic orbitals in a crystal as forming dense 592 00:29:23,000 --> 00:29:26,200 continuous energy bands separated by regions of 593 00:29:26,200 --> 00:29:28,400 forbidden energy called band gaps. 594 00:29:28,800 --> 00:29:31,520 This model immediately explains the difference between reddles, 595 00:29:31,520 --> 00:29:34,040 semiconductors and insulators. It does. 596 00:29:34,160 --> 00:29:37,440 Metals have high conductivity because their valence band is 597 00:29:37,480 --> 00:29:40,480 either partially filled or it overlaps with the conduction 598 00:29:40,480 --> 00:29:42,160 band. So electrons are free to move 599 00:29:42,320 --> 00:29:43,080 and. Insulators. 600 00:29:43,080 --> 00:29:46,280 Insulators have a large band gap, preventing thermal 601 00:29:46,280 --> 00:29:48,760 excitation. Semiconductors, however, have a 602 00:29:48,760 --> 00:29:51,800 small enough band gap that thermal energy can excite some 603 00:29:51,800 --> 00:29:54,760 electrons from the filled valence band into the empty 604 00:29:54,760 --> 00:29:56,640 conduction band. And the movement of those 605 00:29:56,640 --> 00:29:59,760 electrons and the holes they leave behind is what allows 606 00:29:59,760 --> 00:30:01,080 current to flow. Right. 607 00:30:01,120 --> 00:30:04,280 And the key signature is that a semiconductors conductivity 608 00:30:04,280 --> 00:30:06,440 increases exponentially with temperature. 609 00:30:06,440 --> 00:30:08,880 And the true revolution came when we learned to control that 610 00:30:08,880 --> 00:30:12,120 conductivity using extrinsic semiconductors via doping. 611 00:30:12,360 --> 00:30:16,280 Doping allows precise control for N type semiconductors. 612 00:30:16,280 --> 00:30:19,640 We dope with a donor at from a higher group like phosphorus and 613 00:30:19,640 --> 00:30:22,280 silicon. The extra valence electron 614 00:30:22,280 --> 00:30:25,480 creates a filled donor band just below the conduction band, 615 00:30:25,680 --> 00:30:28,200 making electrons the primary charge carriers. 616 00:30:28,200 --> 00:30:29,640 And for P type it's the opposite. 617 00:30:29,640 --> 00:30:33,200 For P type, we dope with an acceptor atom from a lower group 618 00:30:33,200 --> 00:30:35,720 like Boron. The acceptor atom creates an 619 00:30:35,720 --> 00:30:38,200 empty acceptor band just above the valence band. 620 00:30:38,600 --> 00:30:41,840 Electrons jump into it, leaving behind mobile holes in the 621 00:30:41,840 --> 00:30:44,440 valence band which act as the charge carriers. 622 00:30:44,600 --> 00:30:47,520 And this ability to sandwich N type and P type materials 623 00:30:47,600 --> 00:30:50,520 together is the foundation for all modern technology. 624 00:30:50,560 --> 00:30:53,320 All of it. Transistors, LE, DS, solar 625 00:30:53,320 --> 00:30:55,720 cells. The PN junction is essential. 626 00:30:55,960 --> 00:30:59,040 In a solar cell, a photon creates an electron hole pair 627 00:30:59,200 --> 00:31:01,880 and the intrinsic electric field at the junction sweeps them 628 00:31:01,880 --> 00:31:04,640 apart, creating a current. Pulling the structure down to 629 00:31:04,640 --> 00:31:08,040 the nanoscale, what unique properties emerge when we look 630 00:31:08,040 --> 00:31:10,920 at quantum dots? Quantum dots are semiconductor 631 00:31:10,920 --> 00:31:14,320 crystals that are tiny, only a few nanometers in size. 632 00:31:14,960 --> 00:31:17,680 Because the particle size is similar to the wavelength of the 633 00:31:17,680 --> 00:31:20,200 electron hole pair, the electrons and holes are 634 00:31:20,200 --> 00:31:22,960 physically confined. This is the quantum confinement 635 00:31:22,960 --> 00:31:24,680 effect. And that confinement changes the 636 00:31:24,680 --> 00:31:26,880 band gap. It makes the effective band gap 637 00:31:26,960 --> 00:31:30,480 tunable by size. The optical properties the color 638 00:31:30,480 --> 00:31:33,480 of light the dot absorbs and emits can be precisely 639 00:31:33,480 --> 00:31:36,800 controlled just by changing the particle size during synthesis. 640 00:31:37,360 --> 00:31:39,880 Larger dots are redder, smaller dots are bluer. 641 00:31:39,880 --> 00:31:42,040 Which is why they're so revolutionary for displays. 642 00:31:42,040 --> 00:31:44,640 Displays, biological imaging, you name it. 643 00:31:44,760 --> 00:31:48,160 We also looked at the frontier of plasmonic catalysis using 644 00:31:48,160 --> 00:31:51,320 metal nanoparticles. Metal nanoparticles like gold or 645 00:31:51,320 --> 00:31:54,320 silver exhibit surface plasmon resonance when you shine light 646 00:31:54,320 --> 00:31:56,600 on them. This is a collective oscillation 647 00:31:56,600 --> 00:31:59,280 of the surface electrons which results in the generation of 648 00:31:59,280 --> 00:32:02,000 high energy hot electrons and holes. 649 00:32:02,120 --> 00:32:04,080 And these can drive chemical reactions. 650 00:32:04,160 --> 00:32:07,160 They can transfer their energy to reactants, driving reactions 651 00:32:07,160 --> 00:32:09,360 that that would otherwise require high heat, enhancing 652 00:32:09,360 --> 00:32:12,560 catalytic activity in a light assisted process like converting 653 00:32:12,600 --> 00:32:15,880 CO2 into fuels. From ZEET to solar cells, that's 654 00:32:15,880 --> 00:32:18,240 quite the journey. Let's tackle our final pillar, 655 00:32:18,760 --> 00:32:21,120 coordination and organometallic dynamics. 656 00:32:21,120 --> 00:32:23,360 Let's do it. So coordination, chemistry, 657 00:32:23,640 --> 00:32:26,120 ligands donating electrons to a central metal. 658 00:32:26,560 --> 00:32:28,680 The most stable arrangement involves a chelate. 659 00:32:28,800 --> 00:32:32,360 A chelate, yes, polyandentate ligand that forms a ring 660 00:32:32,360 --> 00:32:34,760 structure with a metal centre like the bedentate, 661 00:32:35,040 --> 00:32:38,480 ethyleneamine or an. This field requires rigorous 662 00:32:38,480 --> 00:32:40,560 nomenclature. Give us a quick refresher on the 663 00:32:40,560 --> 00:32:43,440 core rules. OK, cation first, then anion. 664 00:32:43,720 --> 00:32:46,000 Ligands are named first alphabetically. 665 00:32:46,240 --> 00:32:49,080 The metal follows with its oxidation state in Roman 666 00:32:49,080 --> 00:32:51,600 numerals. If the whole complex is an 667 00:32:51,600 --> 00:32:56,520 anion, the metal name gets an 8 suffix and you use prefixes like 668 00:32:56,520 --> 00:32:59,840 bissentrice for complex ligands and the muse symbol for bridging 669 00:32:59,840 --> 00:33:01,280 ligands. And we look at coordination 670 00:33:01,280 --> 00:33:03,000 geometries. The electronic structure of the 671 00:33:03,000 --> 00:33:06,200 metal is often the deciding factor, especially for 672 00:33:06,200 --> 00:33:09,120 coordination #4. For CNN 4 you get 2 main 673 00:33:09,120 --> 00:33:11,120 options. Tetrahedral is common where 674 00:33:11,120 --> 00:33:14,400 stearic repulsion dominates, but square planar geometry is 675 00:33:14,400 --> 00:33:18,120 electronically driven almost exclusively for D8 metal ions 676 00:33:18,120 --> 00:33:21,320 like platinum 2. Why is the D8 configuration so 677 00:33:21,320 --> 00:33:23,360 heavily biased toward square planar? 678 00:33:23,400 --> 00:33:25,800 This is best explained by Ligenfield theory. 679 00:33:26,520 --> 00:33:30,480 In a square planar field, the DX squared minus E squared orbital 680 00:33:30,480 --> 00:33:34,000 is heavily destabilized. For AD 8 complex, the 8 681 00:33:34,000 --> 00:33:37,680 electrons completely fill the four lowest energy D orbitals, 682 00:33:37,920 --> 00:33:40,600 leaving that highest energy 1 completely empty. 683 00:33:41,000 --> 00:33:44,640 This maximizes the stability. What about the less common 684 00:33:44,640 --> 00:33:47,960 coordination #5 complexes? They're often described as 685 00:33:47,960 --> 00:33:50,560 fluxional. CN 5 structures are usually 686 00:33:50,560 --> 00:33:53,200 square, pyramidal or trignal bipyramidal. 687 00:33:53,320 --> 00:33:55,560 They're fluxional because the energy barrier between these two 688 00:33:55,560 --> 00:33:58,720 geometries is very low. The rapid interconversion often 689 00:33:58,720 --> 00:34:01,800 happens through the Berry pseudo rotation mechanism, which is 690 00:34:01,800 --> 00:34:04,160 essentially A symmetrical bending motion where two 691 00:34:04,160 --> 00:34:07,480 Equatorial ligands bend up to become axial and the two axial 692 00:34:07,480 --> 00:34:09,360 ligands flatten out to become Equatorial. 693 00:34:09,360 --> 00:34:12,600 It's a continuous oscillation. And the most common structure CN 694 00:34:12,600 --> 00:34:15,480 6 is octahedral. But even here we see 695 00:34:15,480 --> 00:34:18,120 distortions. The standard octahedral geometry 696 00:34:18,120 --> 00:34:21,280 maximizes symmetry. The most common distortion is 697 00:34:21,280 --> 00:34:25,199 tetragonal distortion, and this is particularly noted for D9 698 00:34:25,199 --> 00:34:28,159 complexes where it arrives rises due to the John Teller effect. 699 00:34:28,520 --> 00:34:31,400 The John Teller theorem. Which predicts that any non 700 00:34:31,400 --> 00:34:35,320 linear molecule in a degenerate electronic state will distort 701 00:34:35,320 --> 00:34:38,440 geometrically to remove that degeneracy and lower the overall 702 00:34:38,440 --> 00:34:40,679 energy. It's another case of stability 703 00:34:40,679 --> 00:34:43,080 driving structure. These geometries allow for 704 00:34:43,080 --> 00:34:47,040 various types of isomerism. The most frequently tested types 705 00:34:47,040 --> 00:34:49,120 are geometrical isomers. Right. 706 00:34:49,120 --> 00:34:53,360 For octahedral complexes of the form MA4B2 you get CIS and trans 707 00:34:53,360 --> 00:34:56,440 isomers. For MA3B3, you get FAC and Mer 708 00:34:56,520 --> 00:34:59,880 isomers depending on whether the three identical ligands occupy a 709 00:34:59,880 --> 00:35:02,160 face or a Meridian of the octahedron. 710 00:35:02,240 --> 00:35:06,000 Complex stability is quantified by the formation constant KF. 711 00:35:06,160 --> 00:35:08,520 Yes, and this measure of stability brings us back to the 712 00:35:08,520 --> 00:35:11,520 chelote effect. We know that a complex formed by 713 00:35:11,520 --> 00:35:15,240 a bidentate chelate ligand like N is vastly more stable than the 714 00:35:15,240 --> 00:35:18,960 complex formed by two equivalent monodentate ligands like 2 715 00:35:18,960 --> 00:35:21,400 ammonia molecules. Even though they form the same 716 00:35:21,400 --> 00:35:25,760 number of metal nitrogen bonds, the bonding enthalpy is similar, 717 00:35:25,760 --> 00:35:27,640 so the stabilization must be entropic. 718 00:35:27,640 --> 00:35:29,560 Can you break that down for us? Certainly. 719 00:35:29,840 --> 00:35:33,480 Let's compare the reactions when you react a metal Aqua complex 720 00:35:33,480 --> 00:35:36,440 with two ammonia molecules. You start with three species on 721 00:35:36,440 --> 00:35:39,080 the left and end with three species on the right. 722 00:35:40,000 --> 00:35:43,000 There is zero net change in the number of particles, so delta S 723 00:35:43,000 --> 00:35:45,800 is about 0. OK, but when you react with one 724 00:35:45,800 --> 00:35:48,400 end molecule, you start with two species on the left and end with 725 00:35:48,400 --> 00:35:51,120 three on the right. The complex +2 water molecules. 726 00:35:51,240 --> 00:35:53,480 So the total number of independent molecules in the 727 00:35:53,480 --> 00:35:56,400 solution increases by 1. It increases. 728 00:35:56,920 --> 00:36:00,480 This greater dispersal of mass and energy results in a positive 729 00:36:00,480 --> 00:36:02,920 and significant delta S for the reaction. 730 00:36:03,400 --> 00:36:08,960 Since delta G equals delta H -, T delta S, that positive entropy 731 00:36:08,960 --> 00:36:12,400 term makes the Gibbs free energy of formation much more negative. 732 00:36:12,440 --> 00:36:14,480 And guarantees greater stability much? 733 00:36:14,480 --> 00:36:16,480 Greater. And the macro cyclic effect 734 00:36:16,480 --> 00:36:18,440 takes this stability even further. 735 00:36:18,560 --> 00:36:22,360 The macro cyclic effect includes that entropic gain plus a 736 00:36:22,360 --> 00:36:24,800 massive additional enthalpic contribution. 737 00:36:25,640 --> 00:36:28,360 Macro cyclic ligands are already pre organized. 738 00:36:28,480 --> 00:36:31,640 They require much less energy to adjust their geometry to fit the 739 00:36:31,640 --> 00:36:35,320 metal, which leads to a highly favorable negative delta H. 740 00:36:36,040 --> 00:36:38,520 We briefly mentioned ligand field theory earlier. 741 00:36:38,880 --> 00:36:41,880 How do ligands fundamentally influence the D orbital 742 00:36:41,880 --> 00:36:45,360 splitting energy delta O? The magnitude of the splitting 743 00:36:45,360 --> 00:36:47,640 energy is dictated by the ability of the ligand to 744 00:36:47,640 --> 00:36:49,920 participate in π bonding with the metal center. 745 00:36:49,920 --> 00:36:51,680 So you have π donors and π acceptors? 746 00:36:51,680 --> 00:36:55,880 Exactly Π Donor ligands like oxide or chloride have filled P 747 00:36:55,880 --> 00:36:59,120 orbitals that interact with the metals T2G orbitals in an anti 748 00:36:59,120 --> 00:37:01,680 bonding fashion. This raises the energy of the 749 00:37:01,680 --> 00:37:05,160 T2G set, which shrinks the overall gap delta O. 750 00:37:05,280 --> 00:37:07,240 Favoring high spin complexes. Right. 751 00:37:07,440 --> 00:37:11,640 Conversely Π acceptor ligands like Co or cyanide have empty π 752 00:37:11,640 --> 00:37:14,560 star orbitals that interact with the metals T2G orbitals in a 753 00:37:14,560 --> 00:37:17,040 bonding fashion. This lowers the energy of the 754 00:37:17,040 --> 00:37:20,360 T2G set, dramatically increasing the gap delta O. 755 00:37:20,520 --> 00:37:24,000 Favoring low spin complexes. And creating very strong fields. 756 00:37:24,200 --> 00:37:27,320 Understanding complex stability leads directly to understanding 757 00:37:27,320 --> 00:37:31,640 the rate of ligand substitution. We classify complexes as lavile 758 00:37:31,640 --> 00:37:34,120 or inert. How do we differentiate the 759 00:37:34,120 --> 00:37:36,600 three core substitution mechanisms? 760 00:37:36,880 --> 00:37:39,080 They're defined by the nature of the intermediate. 761 00:37:39,640 --> 00:37:43,240 A dissociative or D mechanism is where the leaving group departs 762 00:37:43,240 --> 00:37:46,480 first, forming an intermediate with a reduced coordination 763 00:37:46,480 --> 00:37:48,800 number. Bond breaking is rate 764 00:37:48,800 --> 00:37:50,240 determining. An associative. 765 00:37:50,400 --> 00:37:53,800 An associative or a mechanism is where the incoming ligand 766 00:37:53,800 --> 00:37:56,840 attacks first, forming an intermediate with an increased 767 00:37:56,840 --> 00:37:59,760 coordination number. This is highly characteristic of 768 00:37:59,760 --> 00:38:02,880 D8 square planar complexes because they have an empty site 769 00:38:02,880 --> 00:38:05,360 available for attack. And the third one is a mix. 770 00:38:05,520 --> 00:38:08,680 The interchange or I mechanism where bond breaking and 771 00:38:08,680 --> 00:38:10,360 formation happens simultaneously. 772 00:38:10,400 --> 00:38:14,080 It can be ID if bond breaking is more important or IA if bond 773 00:38:14,080 --> 00:38:17,040 formation is more important. Beyond substitution, we must 774 00:38:17,040 --> 00:38:19,920 analyze redox mechanisms. Electron transfer between 2 775 00:38:19,920 --> 00:38:22,680 metal centers. The two paths are inner sphere 776 00:38:22,760 --> 00:38:25,360 and outer sphere. The inner sphere mechanism 777 00:38:25,360 --> 00:38:27,800 requires the formation of a bridging ligand. 778 00:38:28,400 --> 00:38:31,520 One ligand is temporarily shared between the two metal centers, 779 00:38:31,760 --> 00:38:34,320 and the electron transfers through that bridge and outer 780 00:38:34,320 --> 00:38:36,240 sphere. The outer sphere mechanism is 781 00:38:36,240 --> 00:38:39,400 fundamentally different. The complexes just come close to 782 00:38:39,400 --> 00:38:42,360 each other and the electron transfer occurs without any 783 00:38:42,360 --> 00:38:45,760 change to their inner coordination spheres, often via 784 00:38:45,760 --> 00:38:47,640 quantum mechanical electron tunneling. 785 00:38:48,000 --> 00:38:51,320 Marcus theory provides the quantitative framework for outer 786 00:38:51,320 --> 00:38:53,920 sphere rates. This theory is built on the 787 00:38:53,920 --> 00:38:57,360 Frank Condon principle. Why is that principle so crucial 788 00:38:57,360 --> 00:38:59,400 here? The Frank Condon principle 789 00:38:59,400 --> 00:39:02,480 states that because electron movement is nearly instantaneous 790 00:39:02,480 --> 00:39:05,520 compared to nuclear movement, the electron transfer has to 791 00:39:05,520 --> 00:39:08,120 occur while the nuclear geometry is stationary. 792 00:39:08,680 --> 00:39:11,720 But the optimal bond lengths are different for the oxidized and 793 00:39:11,720 --> 00:39:14,720 reduced forms of the metal. So they don't match up. 794 00:39:14,840 --> 00:39:17,400 They don't. Instantaneous electron transfer 795 00:39:17,400 --> 00:39:20,520 would result in a highly unstable product, so the system 796 00:39:20,520 --> 00:39:23,160 has to wait for the reactants to reach a thermodynamically 797 00:39:23,160 --> 00:39:26,600 unstable intermediate nuclear configuration via thermal 798 00:39:26,600 --> 00:39:28,880 fluctuation before the electron can jump. 799 00:39:29,200 --> 00:39:32,280 And the energy required to reach that state is the reorganization 800 00:39:32,280 --> 00:39:35,320 energy Lambda. Right and Lambda has two parts, 801 00:39:35,520 --> 00:39:38,320 the inner sphere reorganization, which is the energy to change 802 00:39:38,320 --> 00:39:42,080 the bond lengths, and the outer sphere reorganization the energy 803 00:39:42,080 --> 00:39:45,320 to reorient the surrounding solvent molecules. 804 00:39:45,320 --> 00:39:47,960 So a bigger structural change means a bigger Lambda. 805 00:39:48,280 --> 00:39:50,160 And a slower electron transfer rate. 806 00:39:50,560 --> 00:39:54,240 We wrap up with Organometallics. Unlike typical coordination 807 00:39:54,240 --> 00:39:57,880 complexes, D metal organometallics strongly adhere 808 00:39:57,880 --> 00:40:01,200 to the 18 electron rule. This is due to the strong Sigma 809 00:40:01,200 --> 00:40:05,320 and π bonding of ligands like Co in octahedral complexes. 810 00:40:05,320 --> 00:40:08,480 These interactions create 9 stable bonding molecular 811 00:40:08,480 --> 00:40:10,960 orbitals. Filling all nine gets you to 18 812 00:40:10,960 --> 00:40:13,880 valence electrons, a pseudo noble gas configuration. 813 00:40:14,080 --> 00:40:17,240 And this adherence to 16 or 18 electrons drives the four 814 00:40:17,240 --> 00:40:20,480 fundamental reactions that form the basis of all organometallic 815 00:40:20,480 --> 00:40:21,840 catalysis. Absolutely. 816 00:40:21,960 --> 00:40:24,600 First oxidative of addition, where the coordination number 817 00:40:24,600 --> 00:40:27,240 and oxidation state of the metal both increase by two. 818 00:40:27,400 --> 00:40:29,040 The reductive elimination, the reverse. 819 00:40:29,160 --> 00:40:32,320 Where both the CN and the oxidation state decrease by two. 820 00:40:32,560 --> 00:40:35,480 And crucially, it only happens if the two fragments are 821 00:40:35,480 --> 00:40:37,880 positioned CIS to one another. And the other two. 822 00:40:37,880 --> 00:40:41,800 Insertion or alcohol migration where neither the CN nor the 823 00:40:41,800 --> 00:40:46,120 oxidation state changes, and simple dissociation or addition 824 00:40:46,120 --> 00:40:48,880 of a ligand where only the CN changes. 825 00:40:48,880 --> 00:40:51,640 And the genius of synthesis is chaining these four steps 826 00:40:51,640 --> 00:40:55,360 together to create a catalytic loop like the Wilkinson catalyst 827 00:40:55,360 --> 00:40:58,160 for hydrogenation. The Wilkinson catalyst cycle is 828 00:40:58,160 --> 00:41:02,320 the perfect textbook example. It relies on a rapid sequence 829 00:41:02,520 --> 00:41:05,680 oxidative addition of hydrogen, followed by the insertion of the 830 00:41:05,680 --> 00:41:09,080 alkene into the metal hydride bond and finally reductive 831 00:41:09,080 --> 00:41:11,440 elimination of the saturated alkene product. 832 00:41:11,440 --> 00:41:14,400 Which returns the catalyst to its starting state for the next 833 00:41:14,400 --> 00:41:16,560 turnover. A perfect demonstration that 834 00:41:16,560 --> 00:41:19,720 mastering the subtle changes in CN and oxidation state is 835 00:41:19,720 --> 00:41:22,040 mastering catalysis. So after all that. 836 00:41:22,040 --> 00:41:26,160 That was a full speed recap of four distinct complex modules. 837 00:41:26,400 --> 00:41:29,920 So what is this entire year of inorganic chemistry truly boiled 838 00:41:29,920 --> 00:41:32,200 down to for you, the student, now that you've seen the map? 839 00:41:32,520 --> 00:41:35,880 It means that every single concept is deeply interwoven. 840 00:41:36,560 --> 00:41:40,600 The properties we defined in module one, ZF size electron 841 00:41:40,600 --> 00:41:44,360 affinity, are not just facts for a quiz, they are the fundamental 842 00:41:44,360 --> 00:41:46,360 constraints that determine stability. 843 00:41:46,440 --> 00:41:49,280 And those constraints flow seamlessly into the predictive 844 00:41:49,280 --> 00:41:52,480 models of Module 2. Why high oxidation states are 845 00:41:52,480 --> 00:41:56,680 stabilized by oxygen, why hard acids prefer fluoride, and how 846 00:41:56,680 --> 00:41:59,400 to use a frost diagram to predict the inherent stability 847 00:41:59,400 --> 00:42:02,520 of any oxidation state. And those chemical drivers then 848 00:42:02,520 --> 00:42:04,640 build the physical world of Module 3. 849 00:42:04,880 --> 00:42:07,640 Determining how ions pack in a crystal and whether the 850 00:42:07,640 --> 00:42:10,800 resulting material is a stable insulator or an electronically 851 00:42:10,800 --> 00:42:14,440 active and type semiconductor. And finally, that stability and 852 00:42:14,440 --> 00:42:17,640 architectural insight is harnessed by Module 4, allowing 853 00:42:17,640 --> 00:42:20,920 us to stabilize unique metal centers, leverage the entropic 854 00:42:20,920 --> 00:42:24,160 power of the plate effect, and program them to perform complex 855 00:42:24,160 --> 00:42:25,560 chemical work. Exactly. 856 00:42:25,640 --> 00:42:28,560 Inorganic chemistry is the chemistry of the entire periodic 857 00:42:28,560 --> 00:42:31,240 table, from fundamental atomic physics to cutting edge 858 00:42:31,240 --> 00:42:34,040 electronic materials. It is the science of stability, 859 00:42:34,040 --> 00:42:37,640 architecture and function. And that, I think, provides our 860 00:42:37,640 --> 00:42:40,480 final provocative thought for you to chew on as you prepare 861 00:42:40,480 --> 00:42:43,440 for your exam. We spend so much time modeling 862 00:42:43,440 --> 00:42:47,680 the ideal system, the perfectly stoichiometric lattice, the pure 863 00:42:47,680 --> 00:42:50,480 metal, the simple valence rules. But remember that the most 864 00:42:50,480 --> 00:42:53,480 exciting, highest impact materials in modern technology, 865 00:42:53,720 --> 00:42:57,320 the defect chemistry that gives gemstones their color, the non 866 00:42:57,320 --> 00:43:01,240 stoichiometric oxides that enable catalysis, the size tune 867 00:43:01,240 --> 00:43:04,760 quantum dots that lit up your displays, They exist precisely 868 00:43:04,760 --> 00:43:06,360 because they embrace imperfection. 869 00:43:06,440 --> 00:43:08,400 Defects are thermodynamically favorable. 870 00:43:08,400 --> 00:43:10,320 They are. They increase entropy, and they 871 00:43:10,360 --> 00:43:14,240 open up pathways for energy and reactivity that perfect systems 872 00:43:14,240 --> 00:43:18,000 simply cannot achieve. Mastery of inorganic chemistry 873 00:43:18,000 --> 00:43:20,440 often means learning to master the defects. 874 00:43:20,680 --> 00:43:22,640 Now go forth and synthesize that knowledge. 875 00:43:22,720 --> 00:43:25,440 And good luck with that exam. Thank you for diving deep with 876 00:43:25,440 --> 00:43:26,360 us. We'll see you next time.