18.Diamond & Graphite: Structure & Properties

Structure: Diamond is a giant covalent structure where each carbon atom is covalently bonded to four other carbon atoms. This forms a regular, rigid 3D lattice.
Hardness: Because of its strong covalent bonds in all directions, diamond is extremely hard and strong.
Melting Point: It has a very high melting point because a huge amount of energy is required to break the strong covalent bonds.
Conductivity: Diamond does not conduct electricity because all its outer electrons are involved in bonding; there are no free (delocalized) electrons or ions to carry a charge.

Structure: In graphite, each carbon atom is bonded to only three other carbon atoms. The atoms are arranged in hexagonal rings that form large, flat layers.
Hardness/Texture: The layers are held together weakly with no covalent bonds between them. This allows the layers to slide over each other, making graphite soft and slippery (ideal for use in pencils and as a lubricant).
Melting Point: Despite being soft, graphite has a very high melting point because the covalent bonds within the layers themselves are very strong.
Conductivity: Since each carbon atom only uses three of its four outer electrons for bonding, one electron is delocalized. These free electrons can move throughout the structure, allowing graphite to conduct electricity and heat.