Lectures 1 & 2

Question 1

Concept of a Localized Bond

Answer 1

Atoms in molecules are connected pairwise by bonds formed by attractive interaction involving valence electrons

Question 2

List

Chemical Bond Types & Meanings

Answer 2

• Nonpolar covalent: equal sharing of bonding pair
• Polar covalent: unequal sharing of bonding pair
• “Ionic Bonding”, transfer of electron (extreme case of polar covalent)

Question 3

How to read electron heat maps

Hot:
Cold:
Names of each type

Answer 3

• Hot: high electron density
• Cold: low electron density
  1. Symmetrical distribution: covalent
  2. Not symmetrical but chill: polar covalent
  3. Basically transfer completely: ionic

Question 4

Rules of Thumb for chemical bond types

Answer 4

1. Metals - nonmetals are generally ionic.
2. nonmetals - generally covalent, polarity determined by electronegativities

Question 5

LDS rules of thumb

Answer 5

1: H is terminal
2. F is terminal
3: Cl, Br, and I are TYPICALLY terminal, can be central atoms in compunds with multiple F and O atoms

Question 6

Formal Charge equation

Answer 6

V - (L + 0.5B)
V: number of valence electrons in free atom
L: number of lone pair electrons (ind.)
B: number of bonding electrons (ind.)

Question 7

VSEPR Rule #1

Answer 7

Regions of high electron density are either bonding or lone pairs which repel one another to minimize electron-electron repulsion.

Erep = q^2 / r12

r12 = instantaneous distance between 1 and 2

Question 8

VSEPR Structure Directions

Answer 8

1. Construct LDS
2. Arrange electron in space so that repulsions are minimized
3. Denote molecular structure from the position of the atoms.

Question 9

VSEPR Shorthand

Answer 9

AXE
1. Central atom is “A”
2. Attached atoms are “X”
3. Lone pairs are “E”

Question 10

VSEPR Rule 2

Answer 10

Electron pairs in multiple bonds are treated the same as single bonds.

Question 11

VSEPR Rule 3

Answer 11

Only consider positions of atoms when reporting shape of a molecule.

Question 12

VSEPR Rule 4

Answer 12

Lone-pair repulsion energies follow as:
(LP-LP) > (LP -B) > (B-B)

LP: lone pair
B: bond

Question 13

VSEPR Rule 5

Answer 13

Lone pairs cause smaller bond angles than expected.

Question 14

Bond Diople Moment Equation

Answer 14

μ = Q × r

μ: strength of dipole moment in debyes
Q: elementary charge (C)
r: bond length (m)

Question 15

One consequence of molecular shape (dipoles)

Answer 15

Symmetric dipole: non-polar
Asymmetric dipoles: polar