The chemical elements that typically form salts include fluorine, chlorine, iodine, bromine and astatine. These elements are commonly referred to as "halogens," comprising group 17, or group VIIA, of the periodic table.
The term "halogen" is derived from the Greek roots "hal-" and "-gen," which when combined, mean "salt former." This designation is attributed to one of the chemical properties of halogens, which refer to their high reactivity with metallic elements in forming salt compounds.
Halogens are poisonous, non-metallic elements that exist in nature as the diatomic molecules F2 for gaseous fluorine, Cl2 for gaseous chlorine gas, I2 for solid iodine and Br2 for liquid bromine. Astatine commonly exists in its monoatomic form, At. Considered to be one of the rarest elements on Earth, astatine radioactively decays only after a few hours of being synthesized. In terms of chemical properties, very little is known about astatine, although scientists think that it behaves similarly to iodine in some aspects.
In aqueous solutions, the halogens produce negatively-charged ions called "halides" in the form of F-, Cl-, I- and Br-. These halide anions are known as fluoride, chloride, iodide and bromide, respectively. Common halide salt compounds include sodium fluoride, stannous fluoride, sodium chloride, silver chloride, silver iodide and lead bromide.