Valence electrons are electrons located furthest away from the nucleus of an atom.
Why are valence electrons important?
Valence electrons are very important because they determine the bonding characteristics of an atom. The bonding characteristics of an atom is largely determined by two factors:
- 1) How many valence electrons there are in an atom
- 2) How far away the valence electrons are from the nucleus of an atom
Valence electrons have the highest principal or main energy level.
- The electron cloud is divided into 7 principal energy levels ( n=1 to n=7).
- If an atom has five (5) energy levels or shells, then the valence electrons are located on energy level five (5), top level.
- Since they have the highest energy, they are able to travel furthest away from the nucleus of an atom.
- Valence electrons are responsible for chemical reactions.
- The number of valence electrons present in an atom determines how reactive an element is.
- Generally atoms are most stable when they have eight valence electrons. This is called the rule of OCTET.
- If an atom has less than eight valence electrons, it will try to gain electrons to fulfil the OCTET rule.
- If an atom has more than eight valence electrons, it will try to lose electrons to fulfil the OCTET rule.
- An atom either transfers or shares electrons with another atom to fulfil the OCTET rule.
- Not all atoms want to fulfil the OCTET rule.
- The smallest element, hydrogen, has only one (1) orbit and the maximum valence electrons it can hold is two (2).
- While hydrogen follows the DUET rule, Boron and Aluminum follow the SEXTET Rule (six valence electrons).
- Valence electrons are very important because they determine the reactivity of an atom, and the type of bond it will form with other elements - covalent or ionic bonds.
(NB: For transition metals, the valence electrons are present in more than one shell and not necessary the outermost shell)