EL - Shapes of molecules

Question 1

What does molecular shape depend on?

Answer 1

The number and type of electron pairs in the outer shell of the central atom.

Question 2

What do electron pairs do to each other and why?

Answer 2

They are all negatively charged so will repel each other to become as far apart as possible.

Question 3

What does the type of electron pair affect in the shape of a molecule?

Answer 3

The type of electron pair effects how much it repels other electron pairs.

Question 4

Which repel more; lone pairs or bonding pairs (of electrons)?

Answer 4

Lone pairs.

Question 5

Where are the greatest bond angles between?

Answer 5

Lone pairs of electrons.

Question 6

Why are bond angles between bonding pairs often reduced?

Answer 6

Because they are pushed together by lone-pair repulsion.

Question 7

Put these bond angle sizes in order from largest to smallest:
Lone-pair/bonding-pair angles.
Lone-pair/lone-pair angles.
Bonding-pair/bonding-pair angles.

Answer 7

Lone-pair/lone-pair angles.
Lone-pair/bonding-pair angles.
Bonding-pair/bonding-pair angles.

Question 8

What is a way of predicting molecular shape?

Answer 8

‘Electron pair repulsion theory’

Question 9

When drawing molecules in 3D, how do you draw the direction of the bonds?

Answer 9

Use a solid triangular wedge to show a bond pointing out of the page towards you and use a broken triangular shape of lines to show a bond pointing into the page away from you.

Question 10

How can you use electron pairs to predict the shapes of molecules?

Answer 10

First you have to draw a dot-and-cross diagram. From this you can then work out how many bonding and non-bonding electron pairs are on the central atom.

Question 11

What shape are molecules with 2 electron pairs on the central atom?

Answer 11

Linear.

Question 12

What shape are molecules with 3 electron pairs on the central atom?

Answer 12

no lone pairs = trigonal planar

1 lone pair = non-linear or ‘bent’

Question 13

What shape are molecules with 4 electron pairs on the central atom?

Answer 13

no lone pairs = tetrahedral
1 lone pair = trigonal pyramidal
2 lone pairs = non-linear or ‘bent’

Question 14

What shape are molecules with 5 electron pairs on the central atom?

Answer 14

no lone pairs = trigonal bipyramidal

Question 15

What shape are molecules with 6 electron pairs on the central atom?

Answer 15

no lone pairs = octahedral

Question 16

For each lone pair, how many degrees do you take from 109.5 degrees to find the bond angle between the bonded pairs?

Answer 16

2.5 degrees for each lone pair.

Question 17

What is the bond angle for a linear molecule?

Answer 17

180

Question 18

What is the bond angle for a non-linear or ‘bent’ molecule with 1 lone pair?

Answer 18

120

Question 19

What is the bond angle for a tetrahedral?

Answer 19

109.5

Question 20

What is the bond angle for a trigonal planar molecule?

Answer 20

120

Question 21

What is the bond angle for a trigonal pyramidal shaped molecule?

Answer 21

107

Question 22

What is the bond angle for a non-linear or ‘bent’ molecule with 2 lone pairs?

Answer 22

104.5

Question 23

What is the bond angle for a trigonal bipyramidal shaped molecule?

Answer 23

90 and 120

Question 24

What is the bond angle for an octahedral?

Answer 24

90