Electrons in subshells

You have already seen that the electrons are arranged in shells with those in incomplete shells becoming involved in bonding.
 

Within each shell is found one or more subshells. The number of subshells in each shell and their letter designations are shown below.
 

Shell	Number of Subshells in the Shell	Letter Designation of Subshell
1	1	s
2	2	s and p
3	3	s, p and d
4	4	s, p, d and f