Valence electrons-

The electros in the outermost orbit of an atom are known as valence electrons.

When the number of valence electron of an atom is less than 4, the material is usually a metal and a conductor.

e.g. - sodium (2, 8,1),  aluminum (2,8,3) etc.

When the number of valence electron of an atom is more than 4, the material is usually a non-metal and an insulator.

e.g. – Nitrogen (2,5), Sulphur (2,8,6) etc.

When the number of valence electron of an atom is 4, the material has both metal and non-metal properties, and is usually a semi-conductor.

e.g. – Silicon (2,8,4) and germanium (2,8,18,4)

Note- The outermost orbit can have a maximum of 8 electrons.