9. Lewis Structures I (Intro to Solid-State Chemistry)

MIT 3.091 Introduction to Solid-State Chemistry, Fall 2018
Instructor: Jeffrey C. Grossman
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Lewis structures, covalent bonds, and resonance.
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[@samuelblackmon493]

According to ptable.com/?lang=en#Properties, Carbon has a higher electronegativity than Hydrogen. Obviously this is not significant when trying to decide the central atom because hydrogen can never be the central atom, but thought I would point this out in case someone may eventually find it useful. It is also of note that Carbon and Hydrogen have similar electronegativities (C = 2.55 and H = 2.20).

[@gregoryb9313]

Look up bifluoride. Its a molecule with H as the central atom F-H-F. Very strange molecule

[@AmitraksharBiszz]

Yes. But Hydrogen is never CENTRAL-ATOM. Just the same way as "Hydrogen's Octet = 2" 💁‍♀ You/One can think of it as an Exception. orrrrr just study Quantum Mechanics pfff.

[@VacentViscera]

I have never had any explanation about bonding and whether they are ionic or covalent or something in between that I have understood better than this. Love this course.

[@ramunasstulga8264]

Then you skipped your classes. Topic starts on 8th grade where they introduce what is ionic and covalent bond therefore it's not the teacher fault that you are skipping classes.

[@VacentViscera]

@@ramunasstulga8264 The key phrase in my post is "that I have understood better than this" which is indicating I'm saying that, while I may have received explanations in the past, such as during 8th grade, those explanations were less well done than the one in the video. This was not a knock against any teachers I had already had, just that the one in this video clicked the most for me.

[@ryanwinter5188]

I would like to make you a shirt and give you that shirt. Great work. Amazing communication.

[@forheuristiclifeksh7836]

41:03

[@AmitraksharBiszz]

TITLE: Lewis Structure (P1), Covalent Bonds (intro), Formal Charce (FC), Electro-negativity ( 𝛘 ) & Covalent Bonds, Dipoles ==================================================================================================== Really SHORT Ver. of Lewis steps 1) Draw/Place Atom-names, central = least_electroNegative (often) 2) Count #Valence-electrons 3) Draw LINEs 4) Draw DOTs ==> make OCTETs, (start @terminal-atoms) 5) If e' left ==> DOTs on central 6) If (central < Octet) ==> use DOTs (from terminal-atoms) ==> make Multiple-Bonds 7) Formal-Charge ==> FC(atom) = OG_Valency - DOTs - LINEs ==================================================================================================== 1. When Atoms Share Electron ==> It's a Covalent Bond ==> We write it:- WITH a DASH @03:35 - 1.1) SHARING ==> UNDER THE HOOD:- @02:50 - 1.2) What happens if we get to something a little bit more complicated, WATER? @04:05 - 1.3) How are electrons shared in Covalent bonds? ===> That is where LEWIS comes in / will help @05:00 2. Lewis Structure P1 - There's a fairly Simple Recipe @05:38 - Water @07:00 - Lone-Pairs / Non-Bonding / Not-Bonding @10:00 - SHAPES NEXT WEEEEEK! @11:00 - Chroline-Oxide-ANION @11:35 - Formaldehyde / Carbonyl-Hydride / Formalin / Methylene oxide @14:20 - Carbon-Dioxide @24:55 - Invoke Step-6 / STROGER SHARING BOND! @17:00 - Multiple seems legit, which one is correct? ==> Formal-Charge (FC) @19:00 3. FC(atom) = #OG_Valency - #dots - #lines @21:00 a) BIGGEST NOTE:- - it is FC(atom) .... not FC(molecule).... ====> i.e. we calculate Formal-Charge on "each individual atom" - OG_Valency:- #Valence-Electrons of that atom that we are calculating Formal-Charge of, before it participated in the bond ===> That atom's neutral (Not ION) #valence-electrons b) UNDER THE HOOD:- - Why not (-2) for each LINE? ==> Bonding Electrons are divided equally between the bonded atoms @21:00 c) What's The Big Deal / Connection to LEWIS? - Lewis-Structure /w set of FCs "closest to zero" (i.e. we count the ABSOLUTE VALUES of FCs) is usually the most stable! - NOTE:- ABSOLUTE VALUES - | FC(atom) | [mathematical absolute values symbol (bars)] d) WHY THIS MATTERS? @25:45 - Has to do it, with ====> HOW IT MOVES ====> with it's VIBRATIONS (wiggling).... (whooooah, not covered in this series) 4. Whole bunch of ROOM in-between POLAR-COVALENT-BOND @28:40 5. 𝛘 = Electro-Negativity (chi / ky) @29:07 => How TIGHTLY the atom is holding on to it's Electrons.... [lavelle.chem.ucla.edu/forum/viewtopic.php?t=81989#p363278] => Electro-Tighten-ity [#REY] => Tendency of an atom to attract a shared pair of electron to itself (in a bond). @29:50 5.1. PAULING:- Arbitrarily Set 𝛘(Fluorine) = 4, he first set 𝛘(Hydrogen) = 2.1 -----------> After years, now it's 𝛘(Hydrogen) = 2.2 a) If the DIfference is High ==> Then that means, One of the Atoms Grabbed the electrons e.g. Δ𝛘(Sodium-Chloride) = 2.23 @33:12 & again @34:40 b) If the DIfference is Zero ==> Then that means, PURE COVALENT BOND Δ𝛘(Chlorine-Diamar) = 0 @34:49 c) If the Diff. is Smwhere in between ==> means, POLAR COVALENT BOND Δ𝛘(Hydrogen-Chloride) = 0.96 @34:52 5.2. There are actually many ElectroNegativity SCALES @32:25 5.3. If the DIfference between this concept (of ElectroNegativity) from One atom to another, is ZERO ==> well, then That Must be a Pure COVALENT BOND! @33:12 5.4. Sodium-Chloride (NaCl) 34:15 5.5. POLAR COVALENT = PARTIALLY IONIC @35:15 GRAPH:- IONIC CHARACTERISTICS PERCENTAGE v/s/ ElectroNegativity @36:00 5.6. a) Δ𝛘 > 2 --> Ionic b) Δ𝛘 < 1.6 --> Polar Covalent c) Δ𝛘 = 0 --> Pure Covalent @36:45 d) Δ𝛘 in Range (1.6 --> 2.0) --> VARIATIONS (either IONIC or POLAR-COVALENT).... in that Intermediate Regime @37:27 5.7. Δ𝛘(NaBr) = Δ𝛘(HF) = 1.9 [Gotta be Carefull] - How Do You KNOW? =================> It's THE PROPERTIES! @38:26 [Remember? I showed you the Properties of Ionic-Solids on Monday] 6. Now, You can Also go further & you can go QUANTITATIVE ==> Dipole @38:50

[@AmitraksharBiszz]

EXTENDED NOTES ==================== 0. recap: Na + Cl ----> IONIC BOND shown /w LewisDots @00:18 - Why did I draw those dots there, & That dot there? -==> They are kinda looking @ each other @00:45 - In an Ionic Bond, - Chlorine is like:- Givme, I want. - Sodium (Na) is like:- Okay, fine, Take it, I'm a plus now - Chlorine is like:- Thank you very much, I'm fully OCTATED! 1. Electron-Sharing Bonds COVALENT-BONDs (Intro) - But see? There is another kind of Bond that can happen.... It's not all about taking & yk... ===> It can also be about sharing @01:18 - If I have HYDROGEN instead, - smth else happens @01:49 - They get kinda closer.... & Closer.... @01:50 - "Not an orbit.... Orbitals (Probability Clouds)" @02:05 - electrons: I don't like you other electron.... You are repelling me - protons:- I don't like you other proton..... you are repelling me - But the electrons do like protons, - so @ a certain point, if you keep bringing these together, yk ====> One electron is like:- well hey, I got an Idea, WHAT IF:- I am attracted to your proton. & You (the other electron) can be attracted to my proton ====> & We'll share, we'll share.... & Thus forms a COVALENT BOND cat-orange-whistling 1.1. SHARING ==> UNDER THE HOOD:- @02:50 - (because of the 1/r proportionality of Attraction/Repulsion) - "When those two HYDROGENs come together, What you get is:- - The Protons -- are a certain distance apart, [That's set by how far you can push them in without them feeling that repulsion] - & Electrons --- as long as they don't get like, "SUPER ON TOP OF EACH OTHER" (because yk, they gon repel each other) ==> THEY'RE HAPPIER.... ==> They are happier -- because they got 2 +ve charges they can kinda go around & be near ==> That leads to happiness ==> LOWER ENERGY BOND! ==> If the total ATTRACTION wins over all the REPULSIONS.... ==> If the Total ENERGY Goes LOWER ==> IF we can have MORE HAPPINESS through Bonding (i.e. that you can calculate if you study Quantum Mechanics) ==> That is when they WILL FORM THE BOND! EXTENDED Version of Point 5. 5. 𝛘 = Electro-Negativity (chi / ky) @29:07 => How TIGHTLY the atom is holding on to it's Electrons.... [lavelle.chem.ucla.edu/forum/viewtopic.php?t=81989#p363278] => Electro-Tighten-ity [#REY] => Tendency of an atom to attract a shared pair of electron to itself (in a bond). @29:50 => How much was it able to pull, those bonding electrons to it - Connected to:- @30:45 a) Size of an Atom How far out electrons are The radius of an Atom b) Whether there's shielding going on. c) How many protons there are? 30:55 d) which atom's gonna want a pair of electron in a bond, which one is gonna want it more & HOW MUCH? @31:03 - Pauling:- I wanna go Further than that, I want to QUANTIFY this @31:10 - Came up with a SCALE @31:22 - The Term "Electro-Negativity" goes long before Pauling, I think Brazilius @31:26 - We are Just gonna Measure Bonding Energies @31:35 5.1. Pauling:- if A bonds to A .... and .... B bonds to B ==> then A to B bonding is not just a simple sum of two @31:41 - He Arbitrarily Set 𝛘(Fluorine) = 4 - Pauling:- set 𝛘(Hydrogen) = 2.1 ===> After years, now it's 2.2 - 𝛘(Cesium) = 0.79 [least electronegative] a.k.a [most electropositive] @32:45 - 𝛘(Fluorine) = 3.98 [most electronegative] 5.2. There are actually many ElectroNegativity SCALES @32:25 - What I want you to know is, What it means Conceptually @32:30 - What I want you to know is, And then how to use it to think about whether a bond is going to be IONIC or COVALENT or smwhere in BETWEEN 5.3. If the DIfference between this concept (of ElectroNegativity) from One atom to another, is ZERO ==> well, then That Must be a Pure COVALENT BOND! @33:12 - Cz Neither one can bring in the Electron-Pair, More than the Other @33:25 - e.g. Chlorine-Diamar @33:30 - Δ𝛘(chlorine-Diamar) = 0 - ==> pure Covalent - That's What Electronegativity Means! @33:46 5.4. Sodium-Chloride (NaCl) 34:15 - Δ𝛘(Sodium-Chloride) = 2.23 [Which is pretty High] @34:30 - ==> IONIC @34:35 a) If the DIfference is High ==> Then that means, One of the Atoms Grabbed the electrons e.g. Δ𝛘(Sodium-Chloride) = 2.23 @33:12 & again @34:40 b) If the DIfference is Zero ==> Then that means, PURE COVALENT BOND Δ𝛘(Chlorine-Diamar) = 0 @34:49 c) If the Diff. is Smwhere in between ==> means, POLAR COVALENT BOND Δ𝛘(Hydrogen-Chloride) = 0.96 @34:52 5.5. POLAR COVALENT = PARTIALLY IONIC = There's Ionic Character! @35:15 - There's a little bit of Ionic Thing going on.... - GRAPH:- IONIC CHARACTERISTICS PERCENTAGE v/s/ ElectroNegativity @ 36:00 5.6. Like AufBau, General Rules.... That Might be Broken @36:45 a) Δ𝛘 > 2 --> Ionic b) Δ𝛘 < 1.6 --> Polar Covalent c) Δ𝛘 = 0 --> Pure Covalent d) Δ𝛘 in Range (1.6 --> 2.0) --> VARIATIONS (either IONIC or POLAR-COVALENT).... in that Intermediate Regime @37:27 5.7. Δ𝛘(NaBr) = Δ𝛘(HF) = 1.9 - HF:- Gas @ Room Temparature ===> Really behaves like a Polar-Covalent Molecule - NaBr:- This really behaves like an Ionic Solid! - How Do You KNOW? It's THE PROPERTIES! @38:26 [Remember? I showed you the Properties of Ionic-Solids on Monday] - & SO I can Look at those (the Ionic-Solid Props) & check them off, yk, "Solid @room temp", etc. ==> & See if, Yk, does this fit the bill? Does this look like an Ionic Solid? @38:34 - HF, Absolutely does not! - So, even tho those two are the same ==> You gotta be carefull in this Intermediate Regime! 6. Now, You can Also go further & you can go QUANTITATIVE ==> Dipole @38:50 6.1. It's called Polar-Covalent Because we Made a Dipole @39:08 6.2. Dipole Moment:- @39:13 - μ = Qr - Q = Partial Charge on bonded atoms [in this case it's literally the charge that was pulled ===> Tendeency to pull that SHARED ELECTRON @39:28] - r = distance between partial charge - "the charge that was pulled" = Remember? in an Ionic-Bond 1 Electron is literally Pulled over from one atom to another atom? ====> Like literally Transferred? - That increases a little Negative Charge on SODIUM (Na) - The Decreases a little Negative Charge on Chlorine (Cl) ==> That means, that I've got a separate PARTICIAL Charge now, (we can visualize/think of it that way) separated by a distance. 6.3. Doing the MATH for NaCl @39:54 [HOW MUCH CHARGE ARE ON THOSE ATOMS] - μ(NaCl) = 9D - 1D = 3.3 * 10^-30 Coulomb*meter - r = 2.36Angstrom - NOW WE CAN FIND ==== Q = μ/r = 1.3*10^-19Coulomb = ~80% of 1-electron's Charge = That's a Pretty Strong Ionic Bond @42:07 - But it's not a 100% - & This is the message that I wanna tell you:- - In reality, We've been talking about ABSOLUTES, "I Fully Took a Charge" ===> NO! You Didn't, You took 80%! - [cz I was given the Dipole-Moment in that Molecule & I can look up the bond distance @41:34] ===> I can actually tell you HOW MUCH CHARGE ARE ON THOSE ATOMS? - If I know those two information.... a) Dipole-Moment, b) Bond-Distance 6.4. In reality, We've been talking about ABSOLUTES, "I Fully Took a Charge" ===> NO! You Didn't, You took 80%! 6.5. Well this is still gonna behave like an IONIC SOLID even at 80%.... (Remember? again I showed you those on Monday) @42:32 - Even tho it's not FULLY IONIC, It's PRETTY DARN IONIC! 6.6. there's More to Lewis.... We'll talk about that on Friday. [Smth called Resonance Structures]

[@brainstormingsharing1309]

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[@michaelgonzalez9058]

A carbon is abundant because of you

[@zeeshan5483]

No race can compare with this people ... They are genius human on earth and among mankind .

[@bandubansode1466]

Hallo I am Indiaian class 12th students from Maharashtra state. I really impressed after saw this leacture and perfectly clear my all miscocepects regarding this Lewis dot structure theory 🙏🙏😊😊

[@shintarokohata8178]

😊

[@mohamedismail6273]

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[@mohamedismail6273]

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[@mohamedismail6273]

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[@vasdgod]

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