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Depending on the type of element, atoms may lose or gain one or more electrons, leaving a net positive or a net negative charge respectively. Charged atoms and groups of atoms of this kind are called ions. Metal atoms tend to form positive ions by losing electrons, and non-metal atoms tend to form negative ions by gaining electrons.

The mechanism which holds the atoms together in a piece of metal is known as the metallic bond. For instance, in chemical shorthand, the statement

M → M+ + e−

tells us that each metal atom (M) releases an electron (e−) to become a metal ion (M+). The electrons are free to wander about, in between the metal ions, forming a ‘sea’ of negative charge around them. Opposite charges attract each other, so the negative electrons provide a continuous attractive force between the positive ions which binds them all together.

metallic bonding

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