Question

Which of the following elements belong to period 3? Write their electronic configuration.
$_3{\text{Li ,}}{{\text{ }}_{16}}{\text{S ,}}{{\text{ }}_2}{\text{He ,}}{{\text{ }}_{15}}{\text{P}}$

Answer 1

The third row of the periodic table contains a total 8 elements, two out of which belong to s-block while the rest of the six belong to p-block. Atomic numbers of third period elements begin from 11 and end on 18.

Complete step by step answer:
Out of the given four elements Sulphur and Phosphorus belong to the third period of the periodic table.
Sulphur belongs to the third period and 16th group. It is a p-block element and is a member of the Oxygen family. Elements of this family are also called chalcogens.

The general electronic configuration of group 16 is ${\text{n}}{{\text{s}}^2}{\text{n}}{{\text{p}}^4}$.
Atomic number of Sulphur is 16. So, the electronic configuration of Sulphur is $1{{\text{s}}^2}{\text{ 2}}{{\text{s}}^2}{\text{ 2}}{{\text{p}}^6}{\text{ 3}}{{\text{s}}^2}{\text{ 3}}{{\text{p}}^4}$.

Phosphorus belongs to the third period and 15th group. It is also a p-block element and is a member of the Nitrogen family. Elements of this family are also called pnicogens.

The general electronic configuration of group 15 is ${\text{n}}{{\text{s}}^2}{\text{n}}{{\text{p}}^3}$.
Atomic number of Phosphorus is 15. So, the electronic configuration of Phosphorus is ${\text{1}}{{\text{s}}^2}{\text{ 2}}{{\text{s}}^2}{\text{ 2}}{{\text{p}}^6}{\text{ 3}}{{\text{s}}^2}{\text{ 3}}{{\text{p}}^3}$.

Hence, from the above given elements, $_{16}{\text{S}}$ and $_{15}{\text{P}}$belong to third period and their electronic configurations are $1{{\text{s}}^2}{\text{ 2}}{{\text{s}}^2}{\text{ 2}}{{\text{p}}^6}{\text{ 3}}{{\text{s}}^2}{\text{ 3}}{{\text{p}}^4}$and ${\text{1}}{{\text{s}}^2}{\text{ 2}}{{\text{s}}^2}{\text{ 2}}{{\text{p}}^6}{\text{ 3}}{{\text{s}}^2}{\text{ 3}}{{\text{p}}^3}$respectively.

Additional information:
Phosphorus is a non-metal from group 15. It is a mineral which is most often found as inorganic phosphate rocks. White phosphorus and red phosphorus are the two main elemental forms of phosphorus. Phosphorus is essential for life as it is a component of many biologically important macromolecules such as DNA, RNA and some proteins.
Sulphur is a non-metal of group 16 and it is bright yellow in colour. It is sometimes found in free elemental form but most often it is found as sulphide or sulphate mineral. It is used on commercial scale production of sulfuric acid, fertilizers and pesticides. Amino acids such as cysteine, methionine and vitamins such as biotin, thiamine contain sulphur.

Note: Both the elements show electronic configuration according to general electronic configurations of their groups. If we know the atomic numbers and general electronic configuration, we can write the electronic configuration of the elements.