A halogen is a group-17 element, such as fluorine, chlorine, bromine, or iodine. These elements commonly form singly charged halide ions and also form covalent compounds.
Their molecular elemental forms and their halide salts have different properties. Across the group, changing atomic size and electronic structure alters bond strengths, polarizability, and redox behavior rather than producing one universal reactivity ranking for every reaction.
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