Chapter 3: 3.2 VSEPR Theory

Question 1

What info do Lewis structures provide? What info do they not provide?

Answer 1

Provide: Arrangement of electrons and atoms in a molecule
Don’t Provide: Information about the three-dimensional structure of a molecule

Question 2

What does VSEPR theory stand for?

Answer 2

Valence Shell Electron Pair Repulsion theory

Question 3

Assumptions of VSEPR theory:
Pairs of electrons both _______ and __________ (_____ _____), occupy the _______ shell of a central atom

Answer 3

Bonding
Nonbonding
Lone pairs
Valence

Question 4

Assumptions of VSEPR theory:
Electron pairs are also called what? What assumption is made about them?

Answer 4

Regions of electron density
Repel each other and spatially position themselves to maximize the separation of the pairs

Question 5

True or False:
Lone pairs exert less repulsive forces than bonding pairs

Answer 5

False, lone pairs exert greater repulsive forces than bonding pairs

Question 6

Are multiple bonds treated as multiple regions of electron density?

Answer 6

No, they are treated as single regions of electron density

Question 7

In AXmEn Notation, what does the A denote?

Answer 7

The central atom

Question 8

In AXmEn Notation, what does the m denote?

Answer 8

The number of atoms, X, bonded to the central atom, A

Question 9

In AXmEn Notation, what does the n denote?

Answer 9

The total number of lone electron pairs, E, on the central atom

Question 10

What is the sum of m + n in AXE Notation equal to?

Answer 10

The total number of regions of electron density around the central atom

Question 11

When drawing:
Line represents…
Dashed wedge represents…
Solid wedge represents…

Answer 11

Line represents bond in the plane of the page
Dashed wedge represents a bond going away from you, behind the page
Solid wedge represents a bond going toward you, out of the page

Question 12

What does VSEPR theory state?

Answer 12

VSEPR theory states that these regions of electron density must spatially position themselves to achieve maximum separation

Question 13

List shapes of electronic arrangements in the format “Regions of density” - “Geometry”

Answer 13

2 - Linear
3 - Trigonal planar
4 - Tetrahedral
5 - Trigonal bipyramidal
6 - Octahedral

Question 14

What molecular shapes are possible for m + n = 2?
List the possible angles

Answer 14

Linear (180 degrees)

Question 15

What molecular shapes are possible for m + n = 3?
List the possible angles

Answer 15

Trigonal Planar (120 degrees)
Bent (<120 degrees)

Question 16

What molecular shapes are possible for m + n = 4?List the possible angles

Answer 16

Tetrahedral (109.5 degrees)
Trigonal Pyramidal (<109.5 degrees)
Bent (<109.5 degrees)

Question 17

What molecular shapes are possible for m + n = 5? List the possible angles

Answer 17

Trigonal bipyramidal (90 and 120 degrees)
See-saw (<90 and <120 degrees)
T shape (<90 degrees)
Linear (180 degrees)

Question 18

What molecular shapes are possible for m + n = 6?List the possible angles

Answer 18

Octahedral (90 degrees)
Square pyramidal (<90 degrees)
Square planar (90 degrees)

Question 19

How do we determine if a molecule is polar or not?

Answer 19

If the dipole vectors cancel out, we have a nonpolar molecule

Otherwise, we have a polar molecule