Electronic Configurations of Atoms
Based upon the rules and sequence of energy levels, one can write the electronic configurations of atoms of some rows of the periodic table.
First Row Elements
The first row of elements contains only two elements hydrogen and helium.
Hydrogen (Z = 1) has only one electron and it goes to 1s orbital. In helium (Z =2) atom, the second electron can also go into 1s orbital. The electrons must have opposite spins, which are shown by arrows pointing up and down.
