CLAS – Chem 1C – Chapter 13 e-mail: benzene4president@gmail.comweb-site: http://clas.sa.ucsb.edu/staff/terri/drop-in ⇒ M/W 11-12, F 10-12 and 2-3 ⇒ SRB 3274 (starts 4/9)

1. Which of the following is ranked correctly in order of increasing electronegativity:a. Cl Br I b. Al Si P c. Li Na K

2. Rank the following bonds in order of increasing polarity. I. C–O II. C–N III. C–F

3. Order the following ions in size from smallest to largest: S2–, Cl– , K+ , Ca2+, Al3+, Te2– a. Ca2+ < K+ < Cl– < S2– < Al3+ < Te2– b. Al3+ < S2– < Cl– < K+ < Ca2+ < Te2– c. Te2– < Ca2+ < K+ < S2– < Cl– < Al3+ d. Cl– < S2– < Al3+ < K+ < Ca2+ < Te2–

e. Al3+ < Ca2+ < K+ < Cl– < S2– < Te2–

4. Estimate the value of ΔH for the following reaction:

5. Draw Lewis structures for the following:a. BeF2 b. PBr3 c. HCN d. H2CO e. ClO4

- f. SO2 g. ICl3

6. Draw the Lewis structures that minimizes formal charge for the compounds in problem 5.

7. Which of the following resonance contributors for N2O is the most stable?

8. Rank the following in order of shortest to longest carbon oxygen bond length:CH3OH CO CO2 CO3

2-

9. Determine the molecular geometry and bond angle for the following:a. CO2 b. NF3 c. ICl3 d. XeCl5

+

10. Which of the following are polar? Circle all that applya. BF3 b. NH3 c. CCl4 d. XeBr4 e. H2CO

Bond

Ave. Bond Energy (kJ/mol)

N–H 391

N–N 160

N=N 418

N≡N 941

F–F 154

H–F 565

Bond Polarity ⇒ uneven distribution of bonding electrons due to a difference in electronegativity

Electronegativity ⇒ the force of attraction towards bonding electrons

Periodic trend Helpful knowledge ⇒ F > O > N ≈ Cl > Br > I > S > C > H ≈ P

Lewis Structure Guidelines:1. Determine the number of valence electrons (group number, add electrons for anions or subtract electrons for cations)2. Determine the central atom(s) – least electronegative element (exception - hydrogen will not be the central atom)3. Draw out structure with single bonds symmetrically – add square brackets and charge for ions4. Put 6 electrons (3 pairs) on each outer atom except hydrogen – put any remaining electrons on the central atom5. Determine if all atoms have what they want ( H ⇒ 2, Be ⇒ 4, B and Al ⇒ 6, and all else ⇒ 8) – if yes you’re done – if

not add a bond for every 2e- that’s missing – the bonding electrons come from an adjacent atoms non-bonded pair – if there’s more than one outer atom with lone pairs to share with the central is called resonance – the real structure is a hybrid of the possible resonance structures

6. Formal Charge = Group number – #bonds – #non-bonded electrons7. Minimizing formal charge ⇒ only possible for molecules with a central atom in period > 2 ⇒ add a double bond

between an outer negative atom and a positive central atom

Resonance structures ⇒ More than one valid Lewis structure where each structure contributes to a hybrid or true structure – structure with minimum formal charge is the most stable and will contribute to the hybrid the most – a (-) formal charge is more stable if on the most EN atom whereas a (+) formal charge is more stable on the least EN atom

Equation: ΔHest = BDE reactants - BDE products

Molecular Polarity ⇒ Molecules are polar or have a non-zero dipole moment if there’s an uneven distribution of bonding electrons. Non-polar molecules have no dipole moment due to an even or symmetrical distribution of bonding electrons

1. Are all of the central atoms the same (if more than one)? a. no ⇒ it’s polar (has a non-zero dipole moment) b. yes ⇒ keep going

2. Are all of the outer atoms the same?a. no ⇒ it’s polar**b. yes ⇒ keep going

3. Does the central atom have lone pairs? a. no ⇒ non-polar b. yes ⇒ keep going

4. Is the molecular geometry linear or square planar? a. no ⇒ polar b. yes ⇒ non-polar

**Molecules with identical atoms on the opposite sides of molecules can cancel each other out ⇒ The following three sets of molecules have the same formula but the left ones are polar while the right ones are non-polar

non-polar polar polar non-polar polar non-polar

Electronic Domains

akaSteric Number

Generic Formula Electronic/Molecular geometry

Picture** ⇒ always polar Bond Angle Hybridization of

central atom

2 AX2E0 Linear/Linear 180° sp

3

AX3E0

Trigonal planar/Trigonal

planar120°

sp2

AX2E1Trigonal planar/

Bent or V-shaped**

<120°

AX4E0Tetrahedral/ Tetrahedral 109.5°

4 AX3E1Tetrahedral/

Trigonal Pyramid**

<109.5° sp3

AX2E2Tetrahedral/

Bent or V-shaped**

<109.5°

AX5E0

Trigonal bipyramid/

Trigonal bipyramid90°/120°

5

AX4E1Trigonal bipyramid

/See-Saw **

<90°/<120°

dsp3

AX3E2Trigonal bipyramid

/T-shaped **

<90°

AX2E3Trigonal bipyramid

/Linear 180°

AX6E0Octahedral/ Octahedral 90°

6 AX5E1Octahedral /Square

pyramid**

<90° d2sp3

AX4E2Octahedral /Square

planar 90°