bonding and strucutre

Question 1

1:41 understand ionic bonding in terms of electrostatic attractions

Answer 1

Ionic bonding: a strong electrostatic attraction between oppositely charged ions.

Question 2

1:42 understand why compounds with giant ionic lattices have high melting and boiling points

Answer 2

Ionic compounds have high melting and boiling points because they have a giant structure with strong electrostatic forces between oppositely charged ions that require a lot of energy to break.

Question 3

1:43 Know when ionic compounds do or do not conduct electricity

Answer 3

Ionic compounds do not conduct electricity when solid.

However, ionic compounds do conduct electricity if molten or in solution.

Question 4

1:44 know what a covalent bond is

Answer 4

A covalent bond is formed between two non-metal atoms by sharing a pair of electrons in order to fill the outer shell.

Question 5

1:45 understand covalent bonds in terms of electrostatic attractions

Answer 5

Covalent bonding: a strong attraction between a shared pair of electrons and two nuclei.

Question 6

1:47 explain why substances with a simple molecular structures are gases or liquids, or solids with low melting and boiling points. The term intermolecular forces of attraction can be used to represent all forces between molecules

Answer 6

simple molecular structure: made up of molecules

Within each molecule are atoms bonded to each other covalently. These covalent bonds inside the molecules are strong.

However, between the molecules are weak forces of attraction that require little energy to break. These forces are not covalent bonds. This is why simple molecular substances such as carbon dioxide have a low boiling point.

During the change of the state of a substance, the covalent bonds within each molecule remain unbroken. Instead it is the weak forces of attraction between the molecules which have been overcome.

Question 7

1:48 explain why the melting and boiling points of substances with simple molecular structures increase, in general, with increasing relative molecular mass

Answer 7

Larger molecules tend to have higher boiling points.

This is because larger molecules (molecules with more mass) have more forces of attraction between them. These forces, although weak, must be overcome if the substance is to boil, and larger molecules have more attractions which must be overcome.

Question 8

1:49 explain why substances with giant covalent structures are solids with high melting and boiling points

Answer 8

Diamond has a high melting point because it is a giant covalent structure with many strong covalent bonds that require a lot of energy to break.

Question 9

1:50 explain how the structures of diamond, graphite and C60 fullerene influence their physical properties, including electrical conductivity and hardness

Answer 9

Allotropes are different forms of the same element. Three different allotropes of carbon are: diamond, graphite and C60 fullerene.

diamond:
- made up of only carbon atoms
- in a giant 3D lattice
- where each of those atoms has a strong covalent bonds to 4 other carbon atoms
- Every one of carbon’s 4 outer electrons is involved in one of these strong covalent bonds
- is extremely hard because it is a giant covalent structure with many strong covalent bonds
- Because it is hard, diamond is used in high speed cutting tools, eg diamond-tipped saws

Graphite:
- made of only carbon atoms
- in a giant structure
- formed of layers where each carbon atom has a strong covalent bond to 3 other carbons
- This means each carbon atom has one electron not involved in a covalent bond
- these electrons form a sea of delocalised electrons between the layers
- Even though it is a non-metal, graphite can conduct electricity because the delocalised electrons are free to move
- Each layer is a giant structure, with weak forces of attraction between the layers
- These layers can easily slide over each other.
- soft and slippery because it has weak forces of attraction between layers
- used as a lubricant and in pencils because it is soft and slippery

C60 fullerene
- simple molecular structure
- made of only carbon atoms
- forms molecules of 60 carbon atoms
The molecule has weak intermolecular forces of attraction between them which take little energy to overcome
- so C60 fullerene has a low melting point, and it is soft
- cannot conduct electricity
- Although in each molecule every carbon is only covalently bonded to 3 others and the other electrons are delocalised, these electrons cannot jump between different molecules

Question 10

1:51 know conductivity of covalent compounds

Answer 10

Electric current is a flow of charged particles that can move.

Covalent compounds do not conduct electricity.

Question 11

1:52 (Triple only) know how to represent a metallic lattice by a 2-D diagram

Answer 11

When metal atoms join together the outer electrons become ‘delocalised’ which means they are free to move throughout the whole structure.

Metals have a giant regular arrangement of layers of positive ions surrounded by a sea of delocalised electrons.

Question 12

1:53 (Triple only) understand metallic bonding in terms of electrostatic attractions

Answer 12

Metallic bonding is the strong electrostatic attraction between positive metal ions and a sea of delocalised electrons.

Question 13

1:54 (Triple only) explain typical physical properties of metals, including electrical conductivity and malleability

Answer 13

Metals are good conductors because they have delocalised electrons which are free to move.

Metals are malleable (can be hammered into shape) because they have layers of ions that can slide over each other.