Diamond and graphite

Carbon is an element in group 4 (IUPAC group 14) of the periodic table. Each carbon atom can form four covalent bonds. This means that carbon atoms can form families of similar compounds that have:

• chains
• rings

Organic compounds are substances that contain carbon. There is a vast array of natural and synthetic organic compounds because of the ability of carbon to form four covalent bonds. Carbon can also form giant covalent structures, including diamond and graphite.

Diamond

Structure and bonding

Diamond has a giant covalent structure in which:

• each carbon atom is joined to four other carbon atoms by covalent bonds
• the carbon atoms have a regular lattice arrangement
• there are no free electrons

Carbon atoms in diamond have a tetrahedral (pyramid-shaped) arrangement

Properties and uses

The rigid structure, held together by strong covalent bonds, makes diamond very hard. This physical property makes diamond useful for cutting tools, such as diamond-tipped glass cutters and oil rig drills.

Graphite

Structure and bonding

Graphite has a giant covalent structure in which:

• each carbon atom is joined to three other carbon atoms by covalent bonds
• the carbon atoms form layers with a hexagonal arrangement of atoms
• the layers have weak forces between them
• each carbon atom has one non-bonded outer electron, which becomes delocalised

Dotted lines model the weak forces between the layers in graphite

Properties and uses

The delocalised electrons are free to move through the structure, so graphite can conduct electricity. This makes graphite useful for electrodes in batteries and for electrolysis.

The layers in graphite can slide over each other because the forces between them are weak. This makes graphite slippery, so it is useful as a lubricant.