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Why do halogen elements occur as diatomic molecules in their free states?
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halogen
Modern version of the periodic table of the elements.
Halogen elements exist as diatomic molecules in their free states because of their specific electronic structure. Each halogen atom possesses seven valence electrons in its outermost shell. According to the octet rule, atoms tend to combine or share electrons to achieve a stable, eight-electron configuration similar to that of the noble gases.123
By forming a covalent bond with another atom of the same element, each halogen atom shares an electron pair, allowing both atoms to attain a complete, stable octet. This sharing of electrons results in a lower total energy for the bonded atoms compared to that of widely separated, individual atoms, which is the fundamental driver for the formation of these diatomic molecules.14