2
Helium; He
1
Hydrogen; H
3
Lithium; Li
4
Beryllium; Be
5
Boron; B
6
Carbon; C
7
Nitrogen; N
8
Oxygen; O
9
Fluorine; F
10
Neon; Ne
11
Sodium; Na
12
Magnesium; Mg
13
Aluminium; Al
14
Silicon; Si
15
Phosphorus; P
16
Sulfur; S
17
Chlorine, Cl
18
Argon; Ar
19
Potassium; K
20
Calcium; Ca