Definition - What does Valence Electron mean?
A valence electron is an electron in an outer shell of an atom that can participate in forming chemical bonds with other atoms. In a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
The presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements. For a main group element, a valence electron can only be in the outermost electron shell. However, in a transition metal, a valence electron can also be in an inner shell.
Corrosionpedia explains Valence Electron
Valence electrons are the electrons in the outermost electron shell of an atom. The number of electrons in an atom's outermost valence shell governs its bonding behavior. That is why elements whose atoms have the same number of valence electrons are grouped together in the Periodic Table. Within each group of metals, reactivity increases when moving downward on the table. Within each group of nonmetals, reactivity decreases with lower positions on the table.
Elements are most stable when they have all eight valence electrons. This is called the octet rule. The only elements that have this electron configuration are the noble gases, thereby they are inert. All other elements gain, lose or share electrons in order to achieve a full set of valence electrons. Non-metals have a strong pull on their valence electrons, so they tend to gain electrons in order to gain stability and become more like a noble gas. Because metals have loose valence electrons, they always lose electrons in order to gain stability. When a metal loses electrons, it has more protons than electrons and is therefore a positive ion.
Valence electrons are also responsible for the electrical conductivity of an element; as a result, an element may be classified as a metal, nonmetal or semiconductor (metalloid). A metal is an element with high electrical conductivity or malleability when in the solid state. A nonmetallic element has low electrical conductivity; it acts as an insulator. A semiconductor has an electrical conductivity that is intermediate between that of a metal and that of a nonmetal.