Molecular Covalent Structures

Essentials

Covalent structures, also referred to as giant covalent structures, are created when many atoms bind together using covalent bonds to form a larger structure.
These structures are massive and contain countless atoms joined together through strong covalent bonds which require a substantial amount of energy to break.
They usually form a regular, repeating pattern or lattice structure.
Examples include diamond, graphite, silicon dioxide, and fullerenes.

Properties of Molecular Covalent Structures

They are typically hard, due to the strength of the covalent bonds that hold the atoms together.
They have high melting and boiling points because the strong covalent bonds require significant energy to be broken.
Most do not conduct electricity since they lack free ions or electrons.
They are generally not soluble in water.

Structure of Diamond

In diamond, each carbon atom is bonded to four other carbon atoms in a tetrahedral arrangement, forming a hard, robust lattice.
It is an excellent transmitter of heat, and is the hardest known natural substance.
Diamond does not conduct electricity as there are no free ions or electrons; all electrons are involved in covalent bonding.

Structure of Graphite

Unlike diamond, graphite atoms are arranged in a layered structure, with each carbon atom bonded to three others in a hexagonal design.
Layers in graphite are held together by weak van der Waals forces, which allow the layers to easily slide over each other, making graphite slippery and useable as a lubricant.
Graphite can conduct electricity as each carbon atom has one delocalised electron free to move and carry an electrical charge.

Structure and Properties of Silicon Dioxide

Silicon dioxide, or silica, has a similar structure to diamond where each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms.
This rigid structure makes silicon dioxide very hard.
Silicon dioxide does not conduct electricity and is not soluble in water.

Fullerenes and Graphenes

Fullerenes, including buckyballs like C60 and carbon nanotubes, are forms of carbon with a slightly different, spherical or tubular covalent structure.
Graphene is a single layer of graphite and is exceptionally strong and lightweight, with excellent electrical conductivity.
Both graphene and fullerenes have potential in numerous scientific and industrial applications such as in nanotechnology and electronics.