C2

Question 1

Why do small covalent molecules have low boiling points?

Answer 1

They have weak intermolecular forces, which don’t require much energy to break

Question 2

Why don’t small covalent molecules conduct electricity?

Answer 2

They don’t have an overall electric charge

Question 3

What is an allotrope?

Question 4

Why do giant covalent structures have high melting and boiling points?

Answer 4

They have many strong covalent bonds which take lots of energy to break

Question 5

Why can’t diamond conduct electricity?

Answer 5

Because all outer electrons are in covalent bonds, there are no delocalised electrons to carry electrical charge.

Question 6

Name 3 properties of graphite

Answer 6

Soft and slippery; very high melting and boiling point; good conductor of electricity

Question 7

Describe the structure of graphite

Answer 7

Each carbon atom is attached to 3 others, and they form hexagonal rings. These rings are arranged into layers, which are arranged on top of each other.

Question 8

Why is graphite soft and slippery?

Answer 8

There are no covalent bonds between the layers in its structure, only weak intermolecular forces, so the layers can slide over each other

Question 9

Why does graphite have high melting and boiling points?

Answer 9

It has a large number of strong covalent bonds

Question 10

Why is graphite a good conductor of electricity and heat?

Answer 10

Each carbon atom has one delocalised electron, which can move around, carrying electrical charge and thermal energy

Question 11

Why are metals good conductors of heat and electricity?

Answer 11

They have delocalised electrons in their structures, which can carry electrical charge and thermal energy

Question 12

What is graphene?

Answer 12

A single layer of graphite; carbon atoms with three covalent bonds each forming hexagons. One atom thick.

Question 13

Name 3 properties of graphene, and explain them

Answer 13

Good conductor of electricity - each carbon atom has one delocalised electron which can move and carry electrical charge. High strength, and high melting and boiling points - large number of strong covalent bonds.

Question 14

Describe the structure of a fullerene

Answer 14

5-7 sided rings forming a tube shape

Question 15

What are some uses of fullerene?

Answer 15

Can deliver drugs into the body, be used as lubricants in machines to reduce friction, and catalyse chemical reactions.

Question 16

What is a carbon nanotube?

Answer 16

Fullerenes in a cylinder with very high length to diameter ratio.

Question 17

Explain some properties of carbon nanotubes.

Answer 17

High tensile strength. Good conductors of electricity and heat due to delocalised electrons.

Question 18

Suggest some uses of carbon nanotubes.

Answer 18

To reinforce materials such as tennis rackets

Question 19

Why are most polymers solid at room temperature?

Answer 19

They have strong intermolecular forces, so lots of energy is required to break them to melt the polymer.

Question 19

List some uses of polymers

Answer 19

Disposable razors, plastic cups, plastic bottles

Question 20

What are polymers?

Answer 20

Thousands of monomers (small, identical molecules) joined together, with extremely strong covalent bonds.

Question 20

What is a repeating unit?

Answer 20

A shorthand representation of polymers, containing a repeating section of the polymer with brackets around it. The covalent bonds on either side must extend out the brackets, and a little ‘n’ occupies just outside and down of the right bracket, representing the large number of repeating units.

Question 21

In ethene, the carbon atoms have double covalent bonds. How many do they have in poly(ethene)?

Answer 21

They carbon atoms have two single covalent bonds; one either side.

Question 22

Describe how metallic bonding works

Answer 22

Atoms arranged in layers, with all outer shell electrons delocalised, forming a ‘sea’. There is a strong electrostatic attraction between the sea of delocalised electrons and the metal ions.

Question 23

Why do metals have high melting and boiling points?

Answer 23

They have strong metallic bonds (between the sea of delocalised electrons and the metal ions), which require lots of energy to break.

Question 24

Why are metals malleable?

Answer 24

The layers of atoms can slide over each other.

Question 25

What is an alloy?

Answer 25

A mixture of metals.

Question 26

Why are alloys hard?

Answer 26

The varying sizes of atoms make it so the layers are no longer level, so it's harder for them to slide over each other.

Question 27

How big is a micrometer and a nanometer?

Answer 27

Micrometer: 1 x 10^-6 meters Nanometer: 1 x 10^-9 meters

Question 28

How large are course particles, fine particles, and nanoparticles?

Answer 28

Course particles: 1 x 10^-5 meters to 2.5 x 10^-6 meters Fine particles: 100-2500 nanometers Nanoparticles: 1-100 nanometers

Question 29

Describe the surface area:volume ratio in nanoparticles. What does this mean?

Answer 29

Very high SA:V. A much smaller quantity of nanoparticles is required for things such as catalysts, electronics and medicines.

Question 30

What is the risk of using nanoparticles in items such as sun cream?

Answer 30

Due to their tiny size, the nanoparticles can be absorbed into the body and its cells. The long-term effects of this are not currently known.

Question 31

State one advantage and limitation of using a dot and cross diagram.

Answer 31

Crosses are used for one atom's electrons and dots for the other's, so you can easily tell where each electron came from. However, you cannot tell the shape of the molecule.

Question 32

State 3 limitations of using a 2D stick diagram

Answer 32

Covalent bonds are expressed as lines, so you can't tell which electron comes from which atom; there is no information on the outer electrons which are not in bonds; the shape of the molecule is not accurately represented.

Question 33

What is the advantage of a 3D stick diagram over a 2D one?

Answer 33

You can see the shape of the molecule.

Question 34

State 1 advantage and 2 disadvantages of a ball and stick diagram.

Answer 34

The ions are clearly visible in 3D, however the ions are shown as widely spaced despite being packed together in reality. Also, the diagram only represents a small part of the lattice.

Question 35

State 1 advantage and 2 disadvantages of a space diagram.

Answer 35

The ions are shown to be packed closely are they are in reality, however, it can be difficult to see the ions in 3D. Also, the diagram only represents a small part of the lattice.

Question 36

What type of structure do ions form? Describe it.

Answer 36

Giant ionic lattices. Every positive ion is surrounded by positive ions, and vice versa. There are strong ionic bonds.

Question 37

Do ionic compounds have high melting points? Why?

Answer 37

Yes - the strong ionic forces (or ionic forces) require lots of energy to break.