Electrons which are present in the outermost shell of an atom are known as “valence electrons” and the number of valence electrons is known as the “valency” of an element.

S.I. No.	Name of element	Valence shell electrons	valency
1	Hydrogen	-1,+1	1
2	Helium	0	0
3	Lithium	+1	1
4	Beryllium	+2	2
5	Boron	-3, +3	3
6	Carbon	+2 , +4	4
7	Nitrogen	-3 ,-2, -1,+1,+2,+3,+4,+5	3
8	Oxygen	-2	2
9	Fluorine	+1,-1	1
10	Neon	0	0
11	Sodium	+1	1
12	Magnesium	+2	2
13	Aluminium	+3	3
14	Silicon	-4,+2,+4	4
15	Phosphorus	-3,+1,+3,+5	3
16	Sulphur	-2,+2,+4,+6	2
17	Chlorine	-1,+1,+2,+3,+4,+5,+7	1
18	Argon	0	0
19	Potassium	+1	1
20	Calcium	+2	2
21	Scandium	+3	3
22	Titanium	+2,+3,+4	4
23	Vanadium	+2,+3,+4,+5	5,4
24	Chromium	+2,+3,+6	2
25	Manganese	+2,+3,+4,+6,+7	7,4,2
26	Iron	+2,+3,+4,+6	2,3
27	Cobalt	+2,+3,+4	3,2
28	Nickel	+1,+2,+3,+4	2
29	Copper	+1,+2,+3	2,1
30	Zinc	+2	2

Contrast Of Valency or Oxidation State Along A Period

As we move from left to right across a period, the number of valence electrons of the elements increases and ranges between 1 to 8.

Contrast Of Valency or Oxidation State Down A Group

While moving down in a group, the number of valence electrons remains constant. Therefore all the elements in a group have the same valency.