Question

The element ‘X’ has 4 shells and its 3d subshell has 6 electrons. (Symbol is not real). What is its group number? Which is the block?

Answer 1

Hint: From the given details we can find out the electronic configuration of the element X. From the electronic configuration, we can identify the orbital in which the last electron enters and this will give us the block in which the element X belongs to.

Complete Solution :
- According to the postulates given by Bohr and Bury the electrons revolve around the centre of an atom (nucleus) in a predictable pathway named orbits. The illustration of the orbits is done by numbers and letters such as K, L, M, N, and O…. and 1, 2, 3, 4…. respectively.
- The electronic configuration of a particular element is the arrangement of electrons in different shells and subshells. It’s given in the question that the element X has 4 shells and its 3d subshell has 6 electrons. Therefore the electronic configuration of X can be written as follows
\[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{6}}4{{s}^{2}}\]

- From the electronic configuration it’s clear that the last electrons or the incoming electrons will enter the d- subshell. Thus the element X will belong to the d block.
- The group number of an element is equal to the sum of electrons present in (n−1) subshell or the penultimate shell and the outermost shell or the valence shell. Here n is the valence shell i.e. 3.
- Therefore the number of electrons in the (n−1) subshell will be 2 and as we can see there are 6 electrons in the 3d valence shell.
\[~Group\text{ }Number = 2 + 6 = 8\]
 Thus the element X belongs to group 8 and d block.

Note: Keep in mind that, there are three rules which dictate the manner in which electrons are filled in atomic orbitals and they are The Aufbau principle, Pauli’s exclusion principle and Hund’s rule of maximum multiplicity. They deal with the energy of atomic orbitals, about quantum numbers and about the spin of electrons.