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UH CHEM 3331 - Resonance, Structure,a nd Acidity
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CHEM 3331 1nd Edition Lecture 2Outline of Last Lecture I. IntroductionII. Electron configurationIII. BondingIV. ElectronegativityOutline of Current Lecture I. Lewis Dot StructuresII. Formal Chargea. Neutralb. Positivec. NegativeIII. Resonance structuresIV. Skeletal formulasV. Acids and bases reviewCurrent LectureI. Lewis Dot StructuresIn the previous notes there were examples given that contained lewis dot structures. These are simply representations that allow you to see the compound and where all the atoms lie. When you draw a lewis dot structure, any shared or transferred e become a straight line connecting ˉthe two atoms. This shows their bonding. If an atom had remaining electrons we place these around the atom that possesses them. These leftover electrons are called lone pairs. For example, methane and methanol. Methane has no leftover electrons. H has the 2e needed to fill its 1s orbital and C has 8e to fulfill its octet. ˉ ˉThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.In methanol, we see that C and H have their octets filled while O needs 2 lone pairs to fulfill its octet. As we can see, two dots that connect atoms together are redrawn as lines an electron pairs thatare not connected to atoms remain as lone pairs on the atom they belong to.To find out how many electrons an atom possesses in its valence (outermost orbital) simply lookat the top of each column there is a number followed by an A. This number is the number of electrons in the valence. These are used for bonding.II. Formal ChargeTo determine the formal charge we have to gain three piece of information.1) Count non-bonding e (nB)ˉ2) Count all bonding e (B)ˉ3) Valence electrons in a neutral atom (V)FC=V-(B/2 + nB)For example, let’s use methane again, CH4C has 4 valence electrons. There are 0 non-bonded electrons and 8 bonded electrons. FC=4-(8/2+ 0)=0 a) Neutral (FC=0)C bonded to 4 other atoms, N bonded to 3 other atoms and a lone pair, O bonded to 2 other atoms and 2 lone pairs, and 7A halogens bonded to 1 other atom and 3 lone pairs.b) Positive (FC>0)Electropositive C bonded to 3 other atoms, electropositive N bonded to 4 other atoms, electropositive O bonded to 3 other atoms and a lone pairs, and electropositive halogens bonded to 2 other atoms and 2 lone pairs.c) Negative (FC<0)Electronegative C bonded to 3 other atoms with 1 lone pair, electronegative N bonded to 2 other atoms with 2 lone pairs, electronegative O bonded to 1 other atom and 3 lone pairs, and electronegative halogens with 4 lone pairs.III. Resonance structuresA resonance is when there are two or more correct lewis dot structures for the same compound. For example, acetate. The first two lewis dot structures are the two possible ways the compound can be arranged. They look almost identical. The last lewisdot structure is the resonance structure or the combination of the two.Delocalization is when the charge is spread out over multiple atoms.Stable or unstable resonance structuresa) Valid Lewis dot structureb) Move only e (not atoms)ˉc) Charge of all resonance structures must be the same, number of lone pairs must be the same.1) Octets on all atoms2) No charge separation is better than structure with charge separation3) – on electronegative atoms and + on electropositive atomsIV. Skeletal formulasSkeletal formulas are simply drawings of lines that change direction when there is a C atom. We assume any undrawn bonds are H. This is the skeletal formula for butane. CH3CH2CH2CH3. The beginning of the line represents a C bonded to 3 H, the next point where two lines connect is another C bonded to 2 H, the one after that is another C bonded to 2 H, andfinally the end of the line is a C bonded to 3 H. V. Acids and Bases ReviewH2O + H2(SO4)  HSO4 + H3O+ ˉH2O is the base, H2(SO4) is the acid, HSO4 is the conjugate base, H3O+ is the conjugate acid.ˉThis equation stands for the equilibrium constant. C and D are products with their corresponding subscripts which are labled here as c and d. A and B are reactants and their corresponding subscripts are abelled as a and b. When using acids and bases this can be simplified to: From the bottom formula we can rearrange this formula to get the equation for pKa: pKa= -log(Ka) A higher Ka means it is a stronger acid. A lower pKa also means it is a stronger acid.For the following reaction, if the anion is stable, then the conjugate acid is _____? (Strong or Weak)HA H+ +A ˉ(Answer to this question will be in the beginning of the next


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UH CHEM 3331 - Resonance, Structure,a nd Acidity

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