2.2.2: Bonding & Structure

Question 1

Ionic bond

Answer 1

Electrostatic attraction between two oppositely charged ions.

Question 2

Groups whose elements form ionic compounds

Answer 2

1
2
6
7

Question 3

Properties of giant ionic structures

Answer 3

• High melting point
• Electrical insulators (except when molten or in solution)
• Brittle
• Soluble in polar molecules

Question 4

Explain why ionic compounds have high melting points

Answer 4

• Must overcome the (almost infinite) electrostatic attractions between ions
• Huge numbers of ions ∴ large amounts of energy needed

Question 5

Explain why ionic compounds are hard and brittle

Answer 5

• Ions locked in fixed position, will not move
• Electrostatic attractions are strong
• Will break if enough energy supplied –> structure becomes misaligned
• Formation of breakage at a discontinuity

Question 6

What determines the way in which the ions are arranged in a lattice?

Answer 6

• Ratio of ions
• Size of ions
• Charge of ions

Question 7

Effect of charge density on energy required to melt ionic compound

Answer 7

Charge density = charge/area

Ions with increased charge density attract more strongly∴more energy required to break electrostatic attraction and melt

Question 8

Explain why ionic compounds dissolve in polar compounds e.g. water

Answer 8

• Solubility depends on overcoming electrostatic energy and replacing it with similarly strong interaction with water
• Need to match energy held in electrostatic attraction with energy given out making new bonds
• If energy out greater than energy required to break ionic bonds then substance will dissolve

Question 9

Covalent bond

Answer 9

A shared pair of electrons. Occurs (generally) between non-metals.

Question 10

Types of covalent structures:

Answer 10

• Giant covalent

* Simple molecular (finite)

Question 11

Examples of giant covalent structures

Answer 11

Silicon dioxide, graphite, diamond

Question 12

Examples of simple molecular structures

Answer 12

Carbon dioxide, water

Question 13

Dative covalent bond

Answer 13

One of the atoms forming the bond donates both the bonding electrons; coordinate bond.

Question 14

All single bonds are _____ bonds

Answer 14

sigma bonds

Question 15

The sharing of electrons between atoms is achieved by:

Answer 15

the overlap of atomic orbitals containing 1 electron each.

Question 16

Properties of simple molecular structures

Answer 16

• Low MBP
• Do not conduct electricity
• Soluble in organic, non polar solvents

Question 17

Which is stronger, π bonds orσ bonds?

Answer 17

• σ bonds are stronger

Question 18

Double bonds are made up of:

Answer 18

1 σ and 1 π bond

Question 19

Explain why simple molecular structures have low MBP

Answer 19

• Weak London forces require little energy to break

Question 20

Explain why simple molecular structures do not conduct electricity

Answer 20

• No free ions/electrons to carry charge

Question 21

Explain why simple molecular structures are soluble in organic solvents

Answer 21

• Not polar so not soluble in polar solvents

* Soluble instead in organic solvents which are non-polar (“like dissolves like”)

Question 22

Properties of Diamond

Answer 22

• Very high MBP
• Very hard
• High density
• Poor thermal/electrical conductivity because electrons held rigidly in very strong covalent bonds

Question 23

Different arrangements of the same element e.g. graphite and diamond

Answer 23

Allotropes

Question 24

Properties of Graphite

Answer 24

• High MBP because strong covalent bonds between carbon atoms require much energy to break
• Conducts electricity because delocalised electron between layers can carry charge across molecule

Question 25

Shapes of covalent molecules determined by:

Answer 25

Valence Shell Electron Pair Repulsion theory

Question 26

Order of repulsion

Answer 26

* Lone pair to lone pair = Most repulsion * Lone pair to bonding pair * Bonding pair to bonding pair = least repulsion

Question 27

Intermolecular forces

Answer 27

Short range forces that exist between (simple covalent) molecules. They are overcome during physical changes (boiling/melting)

Question 28

Intermolecular forces arise from what?

Answer 28

Differential movement of electrons in a molecule relative to nuclei which gives rise to temporary dipoles.

Question 29

Types of intermolecular forces

Answer 29

* Permanent dipole-dipole attractions * London forces: temporary instantaneous mutually induced dipole-dipole attraction * Hydrogen bonding

Question 30

All types of intermolecular forces are comparatively _______ than a typical covalent bond.

Answer 30

weaker

Question 31

Bond angle in tetrahedral

Answer 31

109.5°

Question 32

Bond angle in pyramidal

Answer 32

107.5°

Question 33

Bond angle in linear

Answer 33

180°

Question 34

Bond angle in angular

Answer 34

104.5°

Question 35

Bond angle in octahedral

Answer 35

90°

Question 36

Bond angle in trigonal planar

Answer 36

120°

Question 37

Bond angle in square planar

Answer 37

180° / 90° depending on which bonds

Question 38

Bond angle in trigonal bypyramidal

Answer 38

120° / 90° depending on which bonds

Question 39

Shapes of molecules options

Answer 39

* Linear * Angular * Pyramidal * Tetrahedral * Octahedral * Trigonal planar * Square planar * Trigonal bypyramidal

Question 40

Sigma bonds can arise from:

Answer 40

• Overlap of atomic orbitals containing 1 electron each | • End of overlap of p orbitals

Question 41

Pi bonds arise from

Answer 41

• Sideways overlap of p orbitals above and below the plane of the sigma bond

Question 42

Factors affecting the strength of intermolecular forces (London forces)

Answer 42

* Number of e- in a molecule | * SA of the molecules (larger SA = more IMF)