Chapter 6: Shapes of molecules and intermolecular forces

Question 1

When drawing a 3D shape what does a solid line represent?

Answer 1

a bond in the plane of the paper

Question 2

When drawing a 3D shape what does a solid wedge represent?

Answer 2

comes out of the plane of the paper

Question 3

When drawing a 3D shape what does a dotted wedge represent?

Answer 3

goes into the plane of the paper

Question 4

Why does a lone pair repel more strongly?

Answer 4

as it’s closer to the central atom and occupies more space than a bonded pair

Question 5

What is the increasing repulsion of lone pairs and bond pairs?

Answer 5

bond pair-bond pair
bond pair-lone pair
lone pair-lone pair

Question 6

What happens to the bond angle when a lone pair is introduced?

Answer 6

decreases the bond angle by 2.5 degrees, repels the bond pairs closer together

Question 7

4 bond pairs and 0 lone pairs

Name the shape and bond angle

Answer 7

Tetrahedral
109.5

Question 8

3 bond pairs and 1 lone pair

Name the shape and bond angle

Answer 8

Pyramidal
107

Question 9

2 bond pairs and 2 lone pairs

Name the shape and bond angle

Answer 9

Non-linear/Angular
104.5

Question 10

2 electron pairs/regions

Name the shape and bond angle

Answer 10

Linear
180

Question 11

3 electron pairs/regions

Name the shape and bond angle

Answer 11

Trigonal planar
120

Question 12

6 electron pairs/regions

Name the shape and bond angle

Answer 12

Octahedral
90

Question 13

What is electronegativity?

Answer 13

The ability of an atom to attract the pair of electrons in a covalent bond to itself

Question 14

What is used to compare electronegativity?

Answer 14

Pauling Scale

Question 15

How does Pauling electronegativity value change across the periodic table?

Answer 15

Nuclear charge increases
atomic radius decreases

Question 16

What are the most electronegative atoms?

Answer 16

Oxygen
Fluorine
Chlorine
Nitrogen

Question 17

What is a polar bond?

Answer 17

when bond atoms have different electronegativity values, making the molecule non-symmetrical

Question 18

What is a non-polar bond?

Answer 18

when similar atoms have the same electronegativity so will repel at the same extent and have no net dipole

Question 19

When do permanent dipoles occur?

Answer 19

between molecules containing polar bonds in addition to induced forces

Question 20

Explain the origin of Induced dipoles

Answer 20

• electrons move at high speeds in orbitals
• more electrons on one side of the atom
• one side becomes slightly more negative, the other slightly more positive
• a dipole in one atom can induce a dipole in a neighbouring one

Question 21

How does polar solvents and solubility work?

Answer 21

water molecules attract ions and break down the ionic lattice

Question 22

What are simple molecular lattices?

Answer 22

covalently bonded molecules attracted by intermolecular forces

Question 23

Why do simple molecular lattices have low boiling point?

Answer 23

not a lot of energy is needed to overcome the weak intermolecular forces

Question 24

Why don’t simple molecular lattices conduct electricity?

Answer 24

there are no free charged particles that can move to carry a charge

Question 25

What happens when non-polar simple molecular substances are added to a polar solvent?

Answer 25

there is little interaction between the molecules in the lattice and the solvent as the intermolecular forces within the polar solvent is too strong to be broken

Question 25

What happens when non-polar simple molecular substances are added to a non-polar solvent?

Answer 25

intermolecular forces form between the molecules and solvent which break the intermolecular forces in the simple molecular lattice and making them dissolve

Question 26

When does a simple molecular substance dissolve in both polar and non-polar solvents?

Answer 26

when they have both polar and non polar bonds

Question 27

Why do polar simple molecular substances dissolve in polar solvents?

Answer 27

the polar solute can attract the polar solvent, breaking down the lattice

Question 28

What is hydrogen bonding?

Answer 28

a permanent-dipole interaction between hydrogen and an electronegative atom, nitrogen, oxygen or fluorine

Question 29

Where do hydrogen bonds act?

Answer 29

between a lone pair of electrons on an electronegative atom and hydrogen atom in a different molecule

Question 30

What do hydrogen bonds do to water molecules in a lattice?

Answer 30

they extend outwards, holding water molecules slightly apart forming an open tetrahedral lattice full of holes

Question 31

Why does the density of water decrease on freezing?

Answer 31

due to holes in the open lattice

Question 32

Why is liquid water denser than ice?

Answer 32

the ice lattice collapses when ice melts and the molecules move closer together

Question 33

Why does water have a high melting and boiling point?

Answer 33

the hydrogen bonds need a large quantity of energy to break them

Question 34

Why does water have a high surface tension?

Answer 34

the extra attraction with hydrogen bonds between the molecules just below the surface