C2 - Diamond and Graphite

What is an allotrope?

Different structural forms of the same element in the same physical state.

Examples of carbon allotropes

Diamond, graphite, graphene, fullerenes.

What type of structure do both diamond and graphite have?

Giant covalent structure.

Why are giant covalent structures strong?

Because they consist of many atoms bonded by strong covalent bonds in a regular lattice.

what element is diamond made from

carbon

How many covalent bonds does each carbon atom form in diamond?

Four.

What arrangement does this create in diamond?

A regular 3D lattice.

Why does diamond have a high melting point?

A lot of energy is required to break the many strong covalent bonds.

Why is diamond very hard?

Each carbon atom is bonded to four others in a rigid 3D lattice.

Does diamond conduct electricity?

No.

Why can't diamond conduct electricity?

All outer electrons are used in covalent bonds, so there are no free electrons to carry charge.

How many covalent bonds does each carbon atom form in graphite?

Three.

What arrangement do carbon atoms form in graphite?

Hexagons arranged in flat layers.

How are the layers in graphite held together?

By weak forces between layers (no covalent bonds).

What property does this give graphite?

The layers can slide over each other, making graphite soft and slippery.

Why does graphite still have a high melting point?

Strong covalent bonds within the layers require lots of energy to break.

Why can graphite conduct electricity?

Each carbon atom has one delocalised electron free to move.

What else can graphite conduct besides electricity?

Heat.

What is a single layer of graphite called?

Graphene.

What structures can graphene form?

Spheres and tubes called fullerenes.

What elements make up silicon dioxide (silica)

Silicon and oxygen.

What is the structure of silicon dioxide?

A giant covalent structure with each silicon atom covalently bonded to oxygen atoms in a repeating lattice.

What type of substance is graphite?

A giant covalent substance made from carbon.

How many covalent bonds does each carbon atom form in graphite?

Three.

What shape do the carbon atoms form in graphite?

Hexagonal rings (rings of 6 carbon atoms).

How are the hexagonal rings in graphite arranged?

In layers.

What holds the layers of graphite together?

Weak forces (no covalent bonds between the layers).

Why is graphite soft and slippery?

Because the layers can slide over each other due to weak forces between them.

What is graphite often used for because it is soft and slippery?

As a lubricant in machines.

Does graphite have a high or low melting/boiling point?

Very high.

Why does graphite have a high melting and boiling point?

Because it contains many strong covalent bonds that require lots of energy to break.

Why can graphite conduct electricity and heat?

Because it has delocalised electrons that are free to move.

Where do the delocalised electrons in graphite come from?

Each carbon atom has 4 outer electrons but only uses 3 in bonding, leaving 1 free electron.

How are graphite and metals similar?

Both have delocalised electrons that can move, allowing them to conduct electricity and heat.

Is graphite a metal?

No, graphite is made from carbon, a non-metal.