Chapter 10: Chemical Bonding II: Molecular Shapes, Valence Bond Theory, and Molecular Orbital Theory

Question 1

VSEPR theory

Answer 1

Valence Shell Electron Pair Repulsion theory

Based on electron groups repeling one another through coulombic forces

Question 2

Electron groups

Answer 2

Includes:

Lone pairs
Single bonds
Multiple bonds
Single electrons

Question 3

Effect of lone pairs

Answer 3

Occupy more space on the central atom because electron density is exclusively on the central atom

Make bonding pair angles smaller

Question 4

Bonding v. lone pair repulsion

Answer 4

Bonding-bonding < Lone-bonding < Lone-lone

Question 5

Hatched wedge

Answer 5

Bond “goes into” page

Question 6

Solid wedge

Answer 6

Bond is “coming out of” the page

Question 7

Polar molecule (4)

Answer 7

Must have:

Polar bonds (bond dipole moments)
Unsymmetrical shape (vector addition)

*Lone pairs affect polarity

*Polarity affects intermolecular forces of attraction (“like dissolves like,” boiling points)

Question 8

Dipole moment

Answer 8

µ = qr = partial charges * distance btwn charges

Represented with a vector arrow (pointing toward negative charge)

Question 9

Electron geometry and polarity

Answer 9

Nonpolar (when identical terminals)
Linear
Trigonal planar
Tetrahedral

Polar
Bent
Trigonal pyramidal

Question 10

Valence bond theory (5)

Answer 10

1. # of orbitals combined = # of hybrid orbitals formed
2. Bonds = two half-filled orbitals with spin-pairing electrons overlapped (or a filled orbital over an empty)
3. Interaction = either (a) alignment along axis between atoms or (b) parallel to each other & perpendicular to the interatomic axis
4. Maximizes bonding and stability, minimizes energy
5. Makes new set of degenerate orbitals

Question 11

Hybrid orbitals

Answer 11

Mixture of multiple standard atomic orbitals that correspond more closely to the actual distribution of electrons in chemically bonded atoms

Question 12

Sigma bond (5)

Answer 12

1. Covalent bond that results when the interacting atomic orbitals point along the axis connecting the two bonding nuclei
2. End-to-end overlap
3. Single bond = sigma bond
   Multiple bond = 1 sigma bond + x pi bonds
4. Stronger than pi bonds
5. Free bond rotation is allowed (single bond)

Question 13

Pi bond (5)

Answer 13

1. Covalent bond that results when the bonding atomic orbitals are parallel to each other and perpendicular to the axis connecting the two bonding nuclei
2. Side-by-side orbital overlap
3. pi bond = multiple bonds
4. Weaker than sigma bonds
5. Bond rotation is restricted (double bond)

Question 14

Geometry/angles/hybridization: 2 electron groups (6)

Answer 14

2 bonding groups
0 lone pairs
linear electron geometry
linear molecular geometry
180° bond angles
sp hybridization

Question 15

Geometry/angles/hybridization: 3 electron groups (8)

Answer 15

trigonal planar electron geometry
sp² hybridization

3 bonding groups/0 lone pairs:
trigonal planar molecular geometry
120° bond angles

2 bonding groups/1 lone pair:
bent molecular geometry
<120° bond angles

Question 16

Geometry/angles/hybridization: 4 electron groups (11)

Answer 16

tetrahedral electron geometry
sp³ hybridization

4 bonding groups/0 lone pairs:
tetrahedral molecular geometry
109.5° bond angles

3 bonding groups/1 lone pair:
trigonal pyramidal
<109.5° bond angles

2 bonding groups/2 lone pairs:
bent molecular geometry
<109.5° bond angles

Question 17

Geometry/angles/hybridization: 5 electron groups (14)

Answer 17

trigonal bipyramidal electron geometry
sp³d hybridization

5 bonding groups/0 lone pairs:
trigonal bipyramidal molecular geometry
120° (equatorial) & 90° (axial) bond angles

4 bonding groups/1 lone pair:
seesaw molecular geometry
<120° (equatorial) & <90° (axial) bond angles

3 bonding pairs/2 lone pairs:
t-shaped molecular geometry
<90° bond angles

2 bonding pairs/3 lone pairs:
linear molecular geometry
180° bond angles

Question 18

Geometry/angles/hybridization: 6 electron groups (11)

Answer 18

octahedral electron geometry
sp³d² hybridization

6 bonding groups/0 lone pairs:
octahedral molecular geometry
90° bond angles

5 bonding groups/1 lone pair:
square pyramidal molecular geometry
<90° bond angles

4 bonding pairs/2 lone pairs:
square planar molecular geometry
90° bond angles

Question 19

Molecular orbital theory

Answer 19

Applies Schrödinger’s wave equation to a molecule to calculate a set of molecular orbitals

Electrons belong to whole molecule, as do orbitals (delocalization of electrons)

Question 20

Linear combination of atomic orbitals (LCAO)

Answer 20

Method of adding together atomic orbitals to make molecular obitals using a weighted average

Since orbitals are wave functions –> constructive & destructive interference

Question 21

Bonding molecular orbital

Answer 21

Occurs when wave functions combine constructively

Has lower energy, greater stability than atomic orbitals from formation

Most electron density is between the nuclei

Question 22

Antibonding molecular orbital

Answer 22

Occurs when wave functions combine destructively

Has higher energy and lower stability than atomic orbitals from formation

Most of electron density is outside the nuclei (node between nuclei)

Question 23

Writing MO diagrams (6)

Answer 23

1. # of MOs formed = # of atomic orbitals combined
2. The more stable the bonding MO, the less stable the antibonding MO
3. The filling of MOs proceeds from low to high energies (aufbau principle)
4. Each MO has max of two electrons (Pauli exclusion principle)
5. Use Hund’s rule when adding electrons to MOs of the same energy
6. # electrons in MOs = # electrons on bonding atoms

Question 24

Bond order

Answer 24

Difference between # valence electrons in bonding and antibonding orbitals (divided by two)

Can = 1/2

Higher bond order = stronger (stability & bond energy) and shorter bonds (lenght)

Bond order = 0 = unstable (no bond will form)

Question 25

MO diagrams for second-period homonuclear diatomic molecules

Answer 25

B₂, C₂, N₂ = pi 2p then sigma 2p

O₂, F₂, Ne₂ = sigma 2p then pi 2p

Question 26

MO diagrams for second-period heteronuclear diatomic molecules

Answer 26

More electronegative atom:
lower atomic orbitals
closer to molecular orbitals
nonbonding orbitals remain localized here