Why are valence electrons important? why do elements bond? what are two ways elements complete their valence?

Why are valence electrons important?

Valence electrons are the electrons present farthest from nucleus. These valence electrons are either transferred or shared during a reaction. Some elements like metals donate valence electrons in ionic compound formation, while some like Carbon mutually share thier valence electrons to make a covalent bond. Hence, it is the valence electrons that make any element reactive or unreactive. 

Why do elements bond?

Elements react in order to gain stability. This stability is gained in the form of attaining noble gas configuration either by donating, gaining or mutually sharing their valence electrons. 

What are two ways elements complete their valence?

The two ways are transfer of electrons and mutual sharing of electrons. 

Example:
              Sodium looses one valence electron to obtain Noble gas configuration of Neon which is more stable configuration.
              Chlorine gains one electrons to obtain Noble Gas configuration of Argon which is more stable configuration.
              Carbon mutually shares its four valence electrons with four atoms of Hydrogen having one electron per atom to complete its octet.