Covalent Bonding

Introduction to Covalent Bonds

Atoms form covalent bonds by sharing pairs of electrons.
This electron sharing allows each atom to reach a full outer shell, developing a stable electronic configuration.
Each shared pair of electrons creates one covalent bond.
Non-metal elements typically form covalent bonds.

Simple Covalent Compounds

A compound with covalent bonding is termed a molecular compound.
Molecular compounds often consist of molecules where two or more atoms are bonded covalently.
For example, in a water molecule, there are two covalent bonds between oxygen and each hydrogen atom.
A molecule of methane (CH4) has four covalent bonds, one between carbon and each of the four hydrogen atoms.
The properties of simple molecular compounds include low melting and boiling points due to weak intermolecular forces.

Drawing Covalent Structures

In a dot-and-cross diagram representing covalent bonds, each dot or cross represents a valence electron. Shared electrons (two per covalent bond) may be represented by a pair of dots, a pair of crosses, or a dot and a cross.
For instance, a diagram of a water molecule (H2O) would show shared pairs between oxygen and each hydrogen atom.
Hydrogen, represented by a single dot or cross, contributes one electron to each bond.

Dative (Coordinate) Covalent Bonds

A dative covalent bond, or coordinate bond, occurs when both electrons in a covalent bond come from the same atom.
This type of bond occurs in molecules such as ammonia and carbon monoxide.

Giant Covalent Structures

Giant covalent structures contain many atoms held together by a network of covalent bonds.
Examples of giant covalent compounds include diamond, graphite, and silicon dioxide.
These compounds exhibit high melting and boiling points, and often are hard and strong, except for graphite, which is softer due to its layered structure.

Molecular Shapes

The shape of a molecule is determined by the number of electron pairs surrounding the central atom.
The repulsion between electron pairs leads to distinct geometrical arrangements. For instance, methane forms a tetrahedral shape, while water forms a bent shape.

Covalent Bonds in Organic Compounds

Organic compounds, largely made up of carbon atoms, have many covalent bonds.
Carbon can form four covalent bonds, allowing it to make complex structures, from simple hydrocarbons to large biomolecules.
The type of covalent bond (single, double, or triple) influences the properties of the organic compound.