Question

Taking an example of an element of atomic number 16, explain how the electronic configuration of atoms of that element relates to its position in the modern periodic table and how valency of an element is calculated on the basis of its atomic number.

Answer 1

Hint: The element with atomic number 16 is Sulphur. Position of an element in the modern periodic table is explained on the basis of its period and group. The period of element relates the number of shells of an atom of the given element whereas the group is similar to the number of valence electrons.

Complete step by step solution:
Electronic configuration of an element is the distribution of electrons in atomic/molecular orbitals.
Here in this question, we need to explain the position of an element with atomic number 16 (Sulphur), on the basis of its electronic configuration.
So, we will need to mention electronic configuration of Sulphur, first.
 S is having configuration of

       ${1s}^2{2s}^2{2p}^6{3s}^2{3p}^4$ or $\left[Ne\right]{3s}^2{3p}^4$

From here we can easily see that the number of shells in Sulphur is 3 (viz. 1s in the first shell, 2s and 2p in the second shell, 3s and 3p in the third shell) and hence as I mentioned in the hint, the period of an element is determined by the number of shells of an atom in an element.
Then the next one that we need to determine is the group in which the element exists. Elements in the same group have similar electronic configuration.
We have seen in the hint section that, group is similar to the number of valence electrons.
Valence electrons is the number of electrons present in the outermost shell (last shell/highest n value) of that particular atom.
Here in Sulphur, when we look at the electronic configuration of Sulphur, it is having 6 valence electrons (2 electrons in 3s orbital + 4 electrons in 3p orbital).
So now we easily understand that the group is 6 (VI A) because the no of valence electrons is 6.
Therefore in the modern periodic table , this element is placed in group 16th.
Thus the position of the given element (here sulphur) is given below:

Group	(VI A) 16th	Because valence electrons = 6
Period	3	Because number of shells= 3

The next part of the question is to calculate valency of an element on the basis of its atomic number.
The valency is the number of electrons it accepts or donates. So in case of non-metals
valency = 8 - valence electrons
& in case of metals
Valency = valence electrons
This is because non-metals accept so lacking electrons are only considered.
Sulphur, being a non-metal, its valency is given by
     valency = 8 - valence electrons
Number of valence electrons for Sulphur = 6
Therefore,
Valency = 8-6 = 2.
From the above, we conclude that the period is 3, group is 16 and valency is 2 for this element (atomic number 16).

Note: Elements in the same period will not have similar electronic configuration.We were considering only basic 8 groups (I A, II A, III A, IV A,V A,VI A,VII A and 0). Valency 8 refers to the group 0 and the element must be a Noble Gas.