Depending on the particular subshell which is filled up, the 113 elements are divided into s, p, d and f block elements. The s and p block elements, corresponding to filling up of the outermost shell (the valence shell), show the maximum variation in properties and are placed in the main groups of the periodic table (groups 1, 2 and 13 to 18) and are called representative elements.
s-block – Elements in which last electron enters the s orbital of their outermost shell. Since there is only one orbital in s block which can accommodate two electrons so there are two groups in s block.
- Group 1 (alkali metals), group 2 (alkaline earth metals)
- General electronic configuration : ns1-2 , n = 2-7
p-block – Elements in which last electron enters any one of the three p orbitals. Since p subshell has three orbitals which can accommodate six electrons so there are 6 groups in periodic table.
- Group 13 – 18
- General electronic configuration : ns2 np1-6 , n = 2-7
- group 16 : chalcogens,
- group 17 : halogens
- group 18 : noble gases
Elements of s and p block collectively are called representative elements.
d-block – Elements in which last electron enters any one of the five d orbitals of their respective penultimate shells. Since d subshell has five d orbitals, which can accommodate ten electrons so there are 10 groups in the periodic table.
- Group 3 – 12
- General electronic configuration : (n-1)d ns1-10 , n = 4-7. Since properties of these elements are midway between s and p block. They are called transition elements. An incomplete d subshell in the atom or its stable ion is a pre – Condition for transition elements.
The f block elements correspond to filling up of the prepenultimate shell, show very little variation in properties and are placed separately as lanthanoids and actinoids outside the periodic table. Lanthanum is not a lanthanoid and actinium is not an actinoid.
General electronic configuration : (n-2) f1-14 (n-1) d0-1 ns2 , n = 6-7
There are two series in f block
Lanthanoids (Ce58-Lu71) = 4f orbitals are filled
Actinoids (Th90 -Lr103) = 5f orbitals are filled. They are known as inner transition elements since they form transition series within d block.
