Chemical bonding

A compound [compound: A compound is a substance formed by the chemical union (involving bond formation) of two or more elements. ] consists of two or more atoms from different elements chemically joined together. There are two types of chemical bond:

• covalent bonds
• ionic bonds

Covalent bonds

A covalent bond [covalent bond: A covalent bond between atoms forms when atoms share electrons to achieve a full outer shell of electrons. ] forms when two atoms share a pair of electrons. The atoms involved are non-metals such as carbon, oxygen and hydrogen. They join together to form molecules [molecules: a collection of two or more atoms held together by chemical bonds. The fundamental unit of compounds ].

The animation shows a covalent bond being formed between a hydrogen atom and a chlorine atom, to form a molecule of hydrogen chloride:

Ionic bonds

Atoms can lose or gain electrons in chemical reactions. When they do this they form charged particles called ions [ions: Electrically charged particles, formed when an atom or molecule gains or loses electrons. ].

• Hydrogen atoms and metal atoms can lose electrons to form positively charged ions.
• Non-metal atoms can gain electrons to form negatively charged ions.

Ionic bonds are the forces of attraction between oppositely charged ions in a compound.