Shapes of molecules

Question 1

What determines the shape of a molecule or ion?

Answer 1

The angles at which bonds between atoms form

Question 2

What is the name of the theory which dictates the angles at which bonds will form and the sizes of these angles?

Answer 2

Valence shell electron repulsion theory

Question 3

What does valence shell electron repulsion theory state about shapes of molecules or ions?

Answer 3

The shape of a molecule/ ion is caused by repulsion between the pairs of electrons (both bond pairs and lone pairs) that surround the central atom
Electron pairs arrange themselves around the central atom so that the repulsion between them is at a minimum

Question 4

What does valence shell electron repulsion theory state about the size of the bond angles?

Answer 4

The amount of repulsion between electrons decrease going down:
Lone pair-lone pair
Lone pair-bond pair
Bond pair-bond pair
So you can find the magnitude of how large the bond angles are based on size of repulsion

Question 5

A bond pair of electrons

Answer 5

When 1 orbital in one atom with 1 electron in it overlaps with another orbital with 1 electron in it = bonded pair
Or if 2 electrons from one orbital and an empty orbital in a dative bond

Question 6

A lone pair of electrons

Answer 6

Electrons in the valence shell of an atom which are not overlapped with the orbital of another atom = not bonded or shared

Question 7

How to find the shape of a molecule/ion

Answer 7

Draw dot and cross diagram and find out how many bond pairs and lone pairs in each one
If unsure if it’s a double bond, treat as though it only has one bonded pair of electrons

Question 8

Shape and name for:
Bonded pairs = 2
Lone pairs = 0

Answer 8

Linear
On a straight line

Question 9

Linear bond angle

Answer 9

180°

Question 10

Name and shape for:
Bonded pairs = 3
Lone pairs = 0

Answer 10

Trigonal planar
A flat triangle shape which lays flat on a surface = 2D

Question 11

Trigonal planar bond angle

Answer 11

120° because there are 3 bonds
And it’s flat so forms circle = 120x3 = 360°

Question 12

Name and shape for:
Bonded pairs = 4
Lone pairs = 0

Answer 12

Tetrahedral
Where 2 bonds are flat on the plane but one goes behind and the other is in front

Question 13

Tetrahedral bond angle

Answer 13

109.5°

Question 14

Name and shape for:
Bonded pairs = 5
Lone pairs = 0

Answer 14

Trigonal bipyramidal

Question 15

Trigonal bipyramidal bond angle

Answer 15

2 angles that are 90°
3 angles that are at 120°
One goes behind the plain the over goes in front

Question 16

Name and shape for
Bond pairs = 6
Lone pairs = 0

Answer 16

Octahedral

Question 17

Octahedral bond angle

Answer 17

At 90° and 180°

Question 18

Name and shape for
Bond pairs = 3
Lone pairs = 1

Answer 18

Trigonal pyramidal

Question 19

Trigonal pyramidal bond angle

Answer 19

107° Because Lone pair–bond pair repulsion is greater than bond pair–bond pair repulsion, so the angle is slightly less than 109.5°

Question 20

Name and shape for
Bonded pairs = 2
Lone pairs = 2

Answer 20

V shaped that lies flat on the plane

Question 21

V shape Angel size

Answer 21

104.5°

Question 22

Explanation for v shape angle size

Answer 22

Lone pair–lone pair repulsion is greater than lone pair–bond pair repulsion, so the bond angle is even further depressed from 109.5°, and is slightly less than the 107°