C2.3

Question 1

What is carbon like?

Answer 1

• Atoms have four electrons on their outer shell and can form four covalent bonds.
• A carbon atom can join with other carbon atoms to form chains and rings.

Question 2

What are allotropes?

Answer 2

• Allotropes are different forms of an element in the same state but with different atomic arrangements.

Question 3

What is diamond like?

Answer 3

• Transparent and hard
• Giant covalent structure in which each carbon atom is covalently bonded to four other carbon atoms.
• Strong covalent bonds from shared electrons mean diamond has a very high melting point and is very hard.
• No delocalised electrons so does not conduct electricity.

Question 4

What is graphite like?

Answer 4

• Giant covalent structure in which each carbon atom is covalently bonded to three other carbon atoms. One electron in the outer shell of each atom is not involved in bonding, so it becomes delocalised instead. The delocalised electrons are free to move through the structure of graphite, so it conducts electricity even though it is a non-metal.
• Graphite has a layered structure. The atoms in each layer form hexagonal rings. The many strong covalent bonds in the layers give graphite a very high melting point. However, there are weak intermolecular forces between each layer, so layers can slide over each other easily. This is why graphite is slippery.

Question 5

What is graphene like?

Answer 5

• Graphene is a carbon allotrope that resembles a single layer of graphite.
• Almost transparent, extremely strong and conducts electricity.

Question 6

What are fullerenes like?

Answer 6

Fullerenes form a large family of carbon allotropes in which the molecules are shaped like tubes or balls.
- A nanotube resembles a sheet of graphene rolled into a tube. Nanotubes are strong and are used to reinforce sports equipment.
- A buckyball resembles a sheet of graphene closed to make a hollow ball, but the carbon atoms may be in pentagons as well as hexagons.

Question 7

Energy transfer in melting or boiling

Answer 7

• During melting or boiling, forces of attraction between particles of a substance are overcome.
• Some bonds break going from the solid to liquid state.
• All remaining bonds break going from the liquid to gas state.
• The stronger the bonds, and the more of them there are, the more energy must be transferred from the surroundings to break them.

Question 8

Energy transfer in condensing or freezing

Answer 8

• Bonds form when a substance condenses or freezes
• Some bonds form going from the gas to the liquid state
• Many bonds form going from the liquid to the solid state.
• Stored chemical energy is transferred to the surroundings, usually by heating, when bonds form.

Question 9

Bonds involved in state changes

Answer 9

• Metal - metallic bonding - strong
• Ionic compounds - ionic bonds - strong
• Giant covalent structure - covalent bonds - strong
• Simple molecule - intermolecular forces - weak

Question 10

Nano particle dimensions

Answer 10

• Nanoparticles are 1 - 100 nm across.
• They consist of a few hundred atoms.

Question 11

What gives nanoparticles their useful properties

Answer 11

• A material made from nanoparticles is described as nanoparticulate.
• Nanoparticulate materials have different properties to the same substance in bulk. Some of these properties are due to the very small size of nanoparticles.
• useful for new paints, new cosmetics, medicines.
• Many properties are due to their very large surface area to volume ratio compared with the same substance in bulk.