Question

What is the electronic configuration of an element in its first excited state which is isoelectronic with${{O}_{2}}$?
A.$[Ne]\,\,3{{s}^{2}}3{{p}^{3}}3{{d}^{1}}$
B.$[Ne]\,\,3{{s}^{2}}3{{p}^{4}}$
C.$[Ne]\,\,3{{s}^{2}}3{{p}^{3}}3{{d}^{2}}$
D.$[Ne]\,\,3{{s}^{1}}3{{p}^{5}}$

Answer 1

Isoelectronic species are the molecules that contain the same amount of electrons. Electronic configuration can be written with the noble gas first (which covers the number of electrons in that noble gas), and then the rest of the configuration.

Complete step by step answer:
The electronic configuration of any element is the total number of electrons written in accordance with the filling of energy levels, as proposed in Aufbau principle.
We have been given to find the electronic configuration of an element in its first excited state, meaning the configuration of its outer energy shell from s, p, d, and f. Given that the element is isoelectronic with oxygen molecule${{O}_{2}}$. So it will have the same number of electrons as that in ${{O}_{2}}$.
So, number of electrons in ${{O}_{2}}$= 8$\times$2 = 16 (as 8 is the atomic number of oxygen)
Now, the element with 16 electrons will have the configuration, $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}\,3{{s}^{2}}3{{p}^{4}}$, rounding up the electrons of 1 and 2 s orbitals to the noble gas neon, we have the configuration as $[Ne]\,\,3{{s}^{2}}3{{p}^{4}}$.
Hence, option B with the configuration $[Ne]\,\,3{{s}^{2}}3{{p}^{4}}$ is the correct configuration for the excited state of the element.

Note: The electrons are filled in the orbitals according to the Aufbau principle, whose diagram is as follows, that shows the arrows directed for the start of the filling of electrons.