1. valence electron
Wikipedia definition
2. Valence electronIn chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are their "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds. In a single covalent bond both atoms contribute one valence electron to form a shared pair. For main group elements, only the outermost electrons are valence electrons.
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