Question

Give the name and atomic number of the inert gas atom in which the total number of d- electrons is equal to the difference in numbers of total p and s- electrons.

Answer 1

Hint: In a periodic table, the number of groups is 18 whereas the number of periods is 4. The elements of group 18 are called inert gas elements or a noble gas. They consist of Helium, Neon, Argon, Krypton, Xenon, and Radon. The atomic number is the number of protons that are present in the nucleus of an atom.

Complete step by step answer:
We know that elements in the periodic table are arranged in the increasing order of the number of protons. The inert gas elements have atomic numbers 2, 10, 18, 36, 54, 86 for He, Ne, Ar, Kr, Xe, Rn respectively.The noble gas has the general valence electronic configuration $n{s}^{2}n{p}^6$Let us discuss the electronic configuration of each inert gas element in group 18.
As we know the atomic number of Helium (He) is 2. Its electronic configuration is $1s^2$. We can see that there are no d electrons in it.
We also know that the atomic number of Neon (Ne) is 9 and its electronic configuration is $1s^{2}2s^{2}2p^6$. There are no d electrons. The number of s electrons is 4 and that of p electrons is 6. The difference is $6-4=2$ which is not equal to 0(number of d electrons present here).
Argon with atomic number 18 has the electronic configuration $1s^{2}2s^{2}2p^{6}3s^{2}3p^6$. From the electronic configuration, we can say that there is no d electron. The number of d electrons is 0. The number of s is 6 and that of p is 12. The difference is 6 which is not equal to the number of d electrons here.
For Krypton, the atomic number as we know is 36. The electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^{10}4s^{2}4p^6$.
Here, the number of d electrons $=10$
The number of s electrons $=8$
The number of p electrons $=18$
The difference in the number of s and p electrons is $18-8=10$, which is equal to the number of d electrons present.
Therefore, the inert gas atom is Krypton(Kr) with an atomic number 36.

Note: All the noble gas except Helium has 8 electrons in their valence shell. This is the reason why it is called inert gas. They are usually non-reactive because of the stable electronic configuration. The ${18}^{th}$ group elements do not form compounds under normal conditions.