Question

An element with atomic number 82 belongs to the group.
A.16
B.12
C.14
D.2

Answer 1

Hint: First of all , we will write the electronic configuration of the element . From its electronic configuration we will observe the last electron entering which shell . The value of the principal quantum number of the last shell will give us the period number. The last electron is entering in which subshell i.e. s, p, d, f will give us the knowledge of the block. The number of valence electrons will help us in finding the group number.

Complete answer:
In order to find the position of any element in a group , first of all we will write the electronic configuration of the element according to the aufbau’s principle which states that orbitals with lower atomic energy get filled first. The electronic configuration of the element is: \[\]$1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}3{d^{10}}4{s^2}4{p^6}4{d^{10}}5{s^2}5{p^6}4{f^{14}}5{d^{10}}6{s^2}6{p^2}$
Or we can write is as: $[Xe]4{f^{14}}5{d^{10}}6{s^2}6{p^2}$
We will now observe the last electron entering which shell and the value of the principal quantum number of that shell. The last electron is entering into $6{p^2}$ , the value of principal quantum number is 6.
The period of the element is 6 and it enters into the p-subshell.
For p-subshell, the value of group number is calculated as :
Group number= 12+ number of valence electrons in the last p-shell . That gives us
Group number= 12+2( $6{p^2}$ , 2 electrons in the last p-shell)
Group number=14.
So, The correct answer is (C).

Note: The position of each element in the periodic table is based on its electronic configuration. Position of a few elements was even predicted even before they were found ( based on their configuration). Hence, if provided with its electronic configuration we can predict its position in the periodic table.