Valence electron

Electron in the outer shell of an atom's energy levels

In chemistry and physics, valence electrons are electrons in the outermost shell of an atom, and they can participate in the formation of a chemical bond if the outermost shell is not closed. In a single covalent bond, a shared pair forms with both atoms in the bond each contributing one valence electron. The presence of valence electrons can determine the element's chemical properties, such as its valence—whether it may bond with other elements and, if so, how readily and with how many.

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