6. Shapes Of Molecules And Ions

Question 1

What does VSEPR stand for?

Answer 1

Valence shell electron pair repulsion (theory)

Question 2

What are the VSEPR rules for the shapes of covalent molecules?

Answer 2

• when a molecules forms, the outer shell electrons repel one another
• the shape the molecule takes is that which minimises repulsion between electron pairs
• strength of repulsion is in the order lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair
• multiple covalent bonds can be treated as single bonds in terms of their repulsion

Question 3

Why are lone pair-lone pair repulsions the strongest?

Answer 3

They aren’t involved in covalent bonding and therefore aren’t attracted by the nucleus of another atom

Question 4

What shape will a molecule with 2 bonding pairs and no lone pairs take up?

Answer 4

Linear

Question 5

What shape will a molecule with 3 bonding pairs and no lone pairs take up?

Answer 5

Trigonal planar

Question 6

What shape will a molecule with 4 bonding pairs and no lone pairs take up?

Answer 6

Tetrahedral

Question 7

What shape will a molecule with 5 bonding pairs and no lone pairs take up?

Answer 7

Trigonal bipyramidal

Question 8

What shape will a molecule with 6 bonding pairs and no lone pairs take up?

Answer 8

Octahedral

Question 9

What is the bond angle in linear molecules?

Answer 9

180°

Question 10

Give examples of linear molecules

Answer 10

BCl2, HCl, Cl2, CO2, HCN

Question 11

What is the bond angle in trigonal planar molecules?

Answer 11

120°

Question 12

Give examples of trigonal planar molecules

Answer 12

BCl3, BF3, C2H4, COH2, AlCl3

Question 13

What is the bond angle in tetrahedral molecules?

Answer 13

109.5°

Question 14

Give examples of tetrahedral molecules

Answer 14

NH4^+, CH4, CCl4

Question 15

Describe the shape of trigonal bipyramidal molecules

Answer 15

3 atoms arranged in a trigonal planar arrangement around a central atom (equatorial), and two atoms lying above and below the trigonal plane (axial)

Question 16

What is the bond angle of trigonal planar?

Answer 16

120° equatorial, 90° axial

Question 17

Give an examples of a trigonal bipyramidal molecule

Answer 17

PCl5

Question 18

What is the bond angle in octahedral molecules?

Answer 18

90°

Question 19

Give an example of an octahedral molecule

Answer 19

SF6

Question 20

What is another name for trigonal bipyramidal?

Answer 20

Trigonal biplanar

Question 21

What shape will a molecule with 3 bonding pairs and 1 lone pair take up?

Answer 21

Pyramidal

Question 22

What shape will a molecule with 2 bonding pairs and 2 lone pairs take up?

Answer 22

Bent

Question 23

What shape will a molecule with 4 bonding pairs and 1 lone pair take up?

Answer 23

Seesaw

Question 24

What shape will a molecule with 3 bonding pairs and 2 lone pairs take up?

Answer 24

T shaped

Question 25

What shape will a molecule with 4 bonding pairs and 2 lone pairs take up?

Answer 25

Square planar

Question 26

What is the bond angle in pyramidal molecules?

Answer 26

107°

Question 27

Describe the shape of a pyramidal molecule

Answer 27

Tetrahedral arrangement around central atom, but repulsion between lone pair and bonding pair is greater, pushing H atoms closer together and giving a slightly smaller bond angle than tetrahedral

Question 28

Give examples of tetrahedral molecules

Answer 28

NH3, PH3, AsH3, SbH3, NCl3, PCl3

Question 29

What are the other names of bent molecules?

Answer 29

Non-linear | V shaped

Question 30

What is the bond angle on bent molecules?

Answer 30

104.5°

Question 31

Give examples of bent molecules

Answer 31

H2O, H2S, OF2, H2Te, H2Se

Question 32

Describe the reason why bent molecules take up their shape

Answer 32

Lone pair have greater repulsive force than bonded pairs so molecule takes up shape to minimise repulsion

Question 33

Why does CH3Cl (chloromethane) have a permanent dipole?

Answer 33

Almost entirely due to the C-Cl bond as C-H bond dipoles are very small

Question 34

Why do H2O and NH3 have a permanent dipole?

Answer 34

Several bond dipoles combine to produce a much larger overall permanent dipole

Question 35

Why is there no overall permanent dipole in the likes of CO2 and CCl4?

Answer 35

The shapes of CO2 and CCl4 are the most symmetric way to arrange 2 and 4 identical atoms around a central atom, so the dipoles cancel out to overall produce molecules with no overall permanent dipole

Question 36

What is the bond angle in a seesaw molecule?

Answer 36

102 and 173°

Question 37

What is the bond angle in a tshaped molecule?

Answer 37

175°

Question 38

What is the bond angle in a square planar molecule?

Answer 38

180° and 9°

Question 39

Give examples of a seesaw molecule

Answer 39

SF4

Question 40

Give examples of a tshaped molecule

Answer 40

ClF3

Question 41

Give examples of a square planar molecule

Answer 41

XeF4