The electrons that determine valence – how an atom reacts chemically – are those with the highest energy.įor a main-group element, the valence electrons are defined as those electrons residing in the electronic shell of highest principal quantum number n. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.
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Or the electron can even break free from its associated atom's shell this is ionization to form a positive ion. An energy gain can trigger the electron to move (jump) to an outer shell this is known as atomic excitation. Similar to a core electron, a valence electron has the ability to absorb or release energy in the form of a photon. An atom with one or two electrons fewer than a closed shell is reactive due to its tendency either to gain the missing valence electrons and form a negative ion, or else to share valence electrons and form a covalent bond. Atoms with one or two valence electrons more than a closed shell are highly reactive due to the relatively low energy to remove the extra valence electrons to form a positive ion.
For a main-group element, a valence electron can exist only in the outermost electron shell for a transition metal, a valence electron can also be in an inner shell.Īn atom with a closed shell of valence electrons (corresponding to a noble gas configuration) tends to be chemically inert. In this way, a given element's reactivity is highly dependent upon its electronic configuration. 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. In a single covalent bond, a shared pair forms with both atoms in the bond each contributing one valence electron. In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. Each hydrogen atom has one valence electron and is univalent. Carbon has four valence electrons and here a valence of four.
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