Structure and bonding of carbon

What are allotropes of carbon?

Different physical forms of the same element, carbon, that contain only carbon atoms but have different bonding arrangements, such as diamond and graphite.

How many other carbon atoms does each carbon atom bond to in diamond?

Four. Each carbon atom forms four strong covalent bonds, giving a tetrahedral arrangement.

What is the structure of diamond?

A giant covalent structure in which each carbon atom is covalently bonded to four other carbon atoms, with all bonds identical and very strong.

Why does diamond have a very high melting point?

It has a giant covalent structure with strong covalent bonds between carbon atoms, and these need lots of energy to break.

Why is diamond extremely hard?

Each carbon atom is bonded to four other carbon atoms by strong covalent bonds in a rigid giant covalent structure, so the structure is very hard and dense.

Why does diamond not conduct electricity?

All of the outer shell electrons in each carbon atom are held in the four covalent bonds, so there are no freely moving particles to carry a charge.

Give one use of diamond and the property that makes it suitable.

It is used in cutting tools like drills because it is extremely hard.

How many other carbon atoms does each carbon atom bond to in graphite?

Three. Each carbon atom forms three covalent bonds, forming layers of hexagonal rings.

What happens to the fourth outer electron of each carbon atom in graphite?

It becomes a delocalised electron, free to move along and between the layers and carry charge.

Why does graphite conduct electricity?

Each carbon atom is bonded to three others, leaving one delocalised electron per carbon atom; these free electrons can move through the structure and carry charge.

Why is graphite soft and slippery?

It is arranged in layers; the atoms within a layer are joined by strong covalent bonds, but there are only weak intermolecular forces between the layers, so the layers can slide over each other.

Are the layers in graphite held together by covalent bonds?

No. There are no covalent bonds between the layers; they are held together only by weak intermolecular forces.

Give two uses of graphite and explain each.

It is used in pencils and as a lubricant because its layers slide over each other, and it is used to make inert electrodes for electrolysis because it conducts electricity.

What is graphene?

A single layer of graphite — a sheet of carbon atoms covalently bonded in a continuous hexagonal layer, only one atom thick, so it is essentially a 2D molecule.

Why is graphene extremely strong?

It has an unbroken pattern of strong covalent bonds between the carbon atoms, so it resists breaking even when patches are stitched together.

Why does graphene conduct electricity?

It has delocalised electrons which can move along its surface, allowing it to conduct electricity.

State three properties of graphene.

It is extremely strong but very light, it conducts heat and electricity, and it is transparent and flexible.

Give two uses of graphene.

It is useful in electronics (such as future computer screens) and in making composite materials.

What are fullerenes?

Molecules of carbon atoms with hollow shapes, based on hexagonal rings but which may also contain rings of five or seven carbon atoms.

What is Buckminsterfullerene?

The first fullerene to be discovered, with the formula C60: 60 carbon atoms joined into 20 hexagons and 12 pentagons forming a hollow sphere shaped like a football.

Give two properties of Buckminsterfullerene.

It has a hollow shape and strong covalent bonds, and it is a poor conductor of electricity.

Why is Buckminsterfullerene slippery with a low melting point?

It is made of individual hollow molecules held together only by weak intermolecular forces, which are easily overcome and allow the molecules to slide over each other.

Give two uses of fullerenes.

They can be used for targeted drug delivery, by trapping molecules inside their hollow shapes, and as catalysts, because their huge surface area can trap catalyst molecules.

What is a carbon nanotube?

A cylindrical fullerene formed by rolling a sheet of graphene, with a very high length to diameter ratio.

Why are carbon nanotubes useful for making badminton rackets?

They have high tensile strength and are resistant to breaking or stretching, and they are very light.

Give two uses of carbon nanotubes.

They are useful in electronics and nanotechnology, and in composites and specialised materials, because they conduct electricity and have high tensile strength.

What type of bonding is found in diamond, graphite, graphene and fullerenes?

Covalent bonding — they are all giant covalent or molecular covalent structures made only of carbon atoms.