These elements are diatomic molecules in their natural form. They require one more electron to fill their outer electron shells, and so have a tendency to form a singly-charged negative ion. This negative ion is referred to as a halide ion; salts containing these ions are known as halides.
Many synthetic organic compounds, and a few natural ones, contain halogen atoms; these are known as halogenated compounds. Thyroid hormones contain iodide atoms. Chloride ions play a key role in brain function by mediating the action of the inhibitory transmitter GABA.