A network solid or covalent network solid is a chemical compound

Chemical compound

A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 in which the atoms are bonded by covalent bond

Covalent bond

A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....

s in a continuous network. In a network solid there are no individual molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s and the entire crystal

Crystal

A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

 may be considered a macromolecule

Macromolecule

A macromolecule is a very large molecule commonly created by some form of polymerization. In biochemistry, the term is applied to the four conventional biopolymers , as well as non-polymeric molecules with large molecular mass such as macrocycles...

. Formulas for network solids as those for ionic compound

Ionic compound

In chemistry, an ionic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Usually, the positively charged portion consists of metal cations and the negatively charged portion is an anion or polyatomic ion. Ions in ionic compounds are held together...

s are simple ratios of the component atoms represented by a formula unit

Formula unit

A formula unit in chemistry is the empirical formula of an ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound...

.

Examples of network solids include diamond

Diamond

In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...

 with a continuous network of carbon atoms and silicon dioxide

Silicon dioxide

The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...

 or quartz

Quartz

Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...

 with a continuous three dimensional network of SiO₂ units. Graphite

Graphite

The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...

 and the mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

 group of silicate minerals structurally consist of continuous two dimensional layers covalently bonded within the layer with other bond types holding the layers together.

Properties

• Electrical conductivity: Poor, as there are no free electrons. When molten, unlike ionic compounds, the substance is still unable to conduct electricity as the macromolecule consists of uncharged atoms, not ions as seen in previously mentioned ionic compounds. Contrary to this rule is graphite. Graphite is an allotrope of Carbon. In this allotrope, each atom of Carbon forms three covalent bonds, leaving one electron in each outer orbital de-localised, creating multiple "free electrons" within each plane of Carbon. This grants graphite electrical conductivity.
• Melting point: High, due to the large amount of energy required to rearrange the covalent bonds.
• Hardness: Hard, due to the strong covalent bond throughout the lattice (however, the layers of carbon atoms in graphite can be easily displaced, allowing the substance to be malleable).
• Solubility: Generally insoluble in any solvent due to the difficulty of solvating a very large molecule.