Hydrogen (H) 1s1
2 Helium (He) 1s2
3 Lithium (Li) [He] 2s1
4 Beryllium (Be) [He] 2s2
5 Boron (B) [He] 2s2 2p1
6 Carbon (C) [He] 2s2 2p2
7 Nitrogen (N) [He] 2s2 2p3
8 Oxygen (O) [He] 2s2 2p4
9 Fluorine (F) [He] 2s2 2p5
10 Neon (Ne) [He] 2s2 2p6
11 Sodium (Na) [Ne] 3s1
12 Magnesium (Mg) [Ne] 3s2
13 Aluminium (Al) [Ne] 3s2 3p1
14 Silicon (Si) [Ne] 3s2 3p2
15 Phosphorus (P) [Ne] 3s2 3p3
16 Sulphur (S) [Ne] 3s2 3p4
17 Chlorine (Cl) [Ne] 3s2 3p5
18 Argon (Ar) [Ne] 3s2 3p6
19 Potassium (K) [Ar] 4s1
20 calcium (ca) [Ar] 4s2