Chapter 9: Molecular Geometry and Bonding Theories

Question 1

VSEPR model

Answer 1

• Valence-shell electron-pair repulsion model
• Electron domains are negatively charged and therefore, repel each other
• Best arrangement of electron domains is the one which minimized repulsion among them

Question 2

electron-domain geometry

Answer 2

Concerned with arrangement of ELECTRON DOMAINS around the central atom

Question 3

molecular geometry

Answer 3

Concerned with arrangement of ONLY ATOMS in molecule/ion

-(no nonbonding pairs)

Question 4

Why do nonbonding pairs take up so much space?

Answer 4

They are less attracted to the nucelus

Question 5

Why do nonbonding pairs tend to reduce bond angles?

Answer 5

Electron domains for nonbonding pairs exert greater repulsive forces on adjacent electron domains

Question 6

Electron domains for MULTIPLE bonds exert __(more or less)__ repulsive force on adjacent electron domains than the domains with SINGLE bonds.

Answer 6

greater

Question 7

Where is repulsion greater?

a) When two domains are 90º away from each other
b) When two domains are 120º away from each other

Answer 7

a) 90º

Question 8

An equatorial domain experiences __(greater/less)__ repulsion than an axial domain because _____.

Answer 8

LESS, because domains from nonbonding pairs exert larger repulsions, and nonbonding domains always occupy equatorial positions (trigonal bipyramidal)

Question 9

bond polarity

Answer 9

How equally the electrons in a bond are shared between two atoms

Question 10

dipole moment

Answer 10

• charge separation within a molecule

- depends on the polarities of the individual bonds and the geometry of the molecule

Question 11

bond dipole

Answer 11

dipole moment due to two atoms in a bond

Question 12

Bond dipoles and dipole moments are vectors which means they have a _____.

Answer 12

magnitude and direction

Question 13

valence-bond theory

Answer 13

• Bonding electron pairs are concentrated in regions in between atoms
• Nonbonding electron pairs lie in directed regions of space
• Valence orbitals of two atoms overlap

Question 14

What happens to the potential energy of the system as overlap or orbitals increases?

Answer 14

• Potential energy decreases

- Bond strength increases

Question 15

Antibonding molecular orbital

Answer 15

• Where electrons go if they spend most of their time outside the nuclei of two atoms
• excludes electron density from central region between atoms’ nuclei
• higher energy than atomic orbitals

Question 16

In a pi bond, the overlapping regions lie __above/below__ the inter nuclear axis.

Answer 16

Below

Question 17

constructive combination

Answer 17

-Energy of resulting MO is lower than energy of two original atomic orbitals

Question 18

destructive combination

Answer 18

-When two atomic orbitals are combined in a way that the electron density is cancelled in central region (where two overlap).