The valencies of the first twenty

The valencies the first twenty elements can have.

Atomic number	Element	Symbol	Valency
1	Hydrogen	H	1
2	Helium	He	0
3	Lithium	Li	1
4	Beryllium	Be	2
5	Boron	B	3
6	Carbon	C	4
7	Nitrogen	N	3
8	Oxygen	O	2
9	Fluorine	F	1
10	Neon	Ne	0
11	Sodium	Na	1
12	Magnesium	Mg	2
13	Aluminium	Al	3
14	Silicon	Si	4
15	Phosphorus	P	5, 3
16	Sulphur	S	6, 2
17	Chlorine	Cl	7, 1
18	Argon	Ar	0
19	Potassium	K	1
20	Calcium	Ca	2

Table 3.6 — valencies of the elements with atomic numbers 1 to 20.

Two things to notice

The noble gases are 0. Helium, neon and argon do not combine, so their combining capacity is nothing.

Some have two values. Phosphorus is 5 or 3; sulphur 6 or 2; chlorine 7 or 1. These are the elements with more than one valency.