Question

What are valence electrons?

Answer 1

Valence electrons are the outermost electrons and are therefore at the highest energy level. Because they are the outermost energy levels, they are available to participate in chemical bonding, either ionic or covalent. Valence electrons determine the reactivity of an atom.

Complete Step By Step Answer:
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, 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, such as its valence whether it may bond with other elements and, if so, how readily and with how many. In this way, a given element's reactivity is highly dependent upon its electronic configuration. 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.

Note:
The number of valence electrons of an element can be determined by the periodic table group (vertical column) in which the element is categorized. With the exception of groups $3 - 12$ (the transition elements), the unit digit of the group number identifies how many valence electrons are associated with a neutral atom of an element listed under that particular column. The valence shell is the set of orbitals which are energetically accessible for accepting electrons to form chemical bonds.