C2.2 Structure and Properties

Question 1

Explain why NaCl is a solid at room temperature

Answer 1

It has a giant ionic lattice
It is held together by ionic bonds which are very strong
Therefore it has a high melting point

Question 2

Explain why oxygen is a gas at room temperature

Answer 2

It has a simple molecular structure
It is held together by weak intermolecular forces
Therefore it has a low melting point

Question 3

Explain why iron is a solid at room temperature

Answer 3

It has a giant metallic structure
It is held together by strong metallic bonds
Therefore it has a high melting point

Question 4

Explain why iron conducts electricity as a solid and liquid

Answer 4

It has delocalised electrons which are free to move throughout the metal structure

Question 5

Explain why graphite conducts electricity

Answer 5

Each carbon has only 3 bonds.
This leaves one delocalised electron
Which is free to move

Question 6

Explain why diamond doesn’t conduct electricity

Answer 6

Each carbon has 4 bonds.

It has no free electrons

Question 7

Explain why sodium chloride doesn’t conduct electricity as a solid

Answer 7

The ions can’t move

Question 8

Explain why sodium chloride conducts electricity when dissolved

Answer 8

The ions are free to move

Question 9

Explain why carbon dioxide doesn’t conduct electricity

Answer 9

Its electrons aren’t free to move

Question 10

Explain why molten magnesium chloride can conduct electricity

Answer 10

The ions are free to move

Question 11

Explain why ammonia is a gas at room temperature

Answer 11

It is a simple molecular substance
Its held together by weak intermolecular forces
Therefore it has a low melting point

Question 12

Explain why methane is a gas at room temperature

Answer 12

It is a simple molecular substance
It is held together by weak intermolecular forces
Therefore it has a low melting point

Question 13

Explain why silicon dioxide has an unusually high melting point

Answer 13

It has a giant covalent structure
It has strong covalent bonds
Which require a lot of energy to break

Question 14

Explain why graphite has a very high melting point

Answer 14

It has a giant covalent structure
which is held together by strong covalent bonds
which require a lot of energy to break

Question 15

What property makes diamond useful for sharpening knives

Answer 15

It is very hard

Question 16

Explain why diamond is so hard

Answer 16

It is arranged in a giant lattice
Each carbon has 4 bonds
The lattice is rigid

Question 17

Explain why thermosetting polymers have high melting points

Answer 17

They have crosslinks between the chains
made with covalent bonds
which are strong

Question 18

Explain why high density polyethene has a higher melting point than low density polyethene

Answer 18

High density polyethene has a crystalline structure and strong forces between the polymer chains

Question 19

What is a nanoparticle

Answer 19

a particle between 1nm and 100nm in size

Question 20

Why do nanoparticles have different properties?

Answer 20

Because they have a much bigger surface area

Question 21

What are the risks of nanoparticles?

Answer 21

Their large surface area makes them very reactive/explosive (nano aluminium)
Nanoparticles are easily absorbed by the lungs and there is little research into the long term health risks.

Question 22

What conditions can be changed to make High Density Polyethene rather than Low Density Poly Ethene?

Answer 22

Pressure

Temperature