Electronic structure 1

The first shell can accommodate up to 2 electrons before it is full.
The second shell can accommodate up to 8 electrons before it is full.
The third shell can accommodate up to 8 electrons before the fourth shell starts to fill.
For example, sodium has 2 electrons in the first shell, 8 in the second and 1 in the third shell so its electronic configuration is written 2,8,1.
For GCSE you will not be asked to give the full electronic structure of an atom or ion with more than 20 electrons.
Group number = number of outer shell electrons.
Period number = number of occupied shells.

Complete the electronic configurations in the table below. The configuration for 11 electrons (Na) is given as an example.

Electron number and configuration	Examples
0 electrons	H⁺
1 electron	H
	H
2 electrons	He, Li⁺, Be²⁺, H^-
	He, Li⁺, Be²⁺, H^-
3 electrons	Li
	Li
4 electrons	Be
	Be
5 electrons	B
	B
6 electrons	C
	C
7 electrons	N
	N
8 electrons	O
	O
9 electrons	F
	F
10 electrons	Ne, Na⁺, Mg²⁺, Al³⁺,F^-, O^2-, N^3-
	Ne, Na⁺, Mg²⁺, Al³⁺,F^-, O^2-, N^3-
11 electrons	Na
2,8,1	Na
12 electrons	Mg
	Mg
13 electrons	Al
	Al
14 electrons	Si
	Si
15 electrons	P
	P
16 electrons	S
	S
17 electrons	Cl
	Cl
18 electrons	Ar, K⁺, Ca²⁺,Cl^-, S^2-, P^3-
	Ar, K⁺, Ca²⁺,Cl^-, S^2-, P^3-
19 electrons	K
	K
20 electrons	Ca
	Ca