One evening last summer, as I strolled along the promenade in Limbe, a small, scenic port town in southwestern Cameroon, I was stopped by a well-dressed young man who greeted me warmly and took me by the hand.
Phosphorus has 3 shells. The outer shell contains 5 electrons. The electronic configuration is :- <br /> 1s2, 2s2, 2p6, 3s2, 3p3.
Magnesium has a total of 12 electrons, so if we draw the electrons for Magnesium, you will have 3 shells. The first shell and second shell will be occupied by the maximum number of electrons. The third shell will occupied by the remaining 2. Therefore, Magnesium has 2 valence electrons.