Question

What is the ground-state electronic configuration of $Se$.

Answer 1

Selenium is a chemical element with the symbol $Se$ and atomic number $34$. It's a nonmetal (rarely referred to as a metalloid) with properties that fall somewhere between sulfur and tellurium in the periodic table, as well as arsenic. In the Earth's crust, it is rarely found in its elemental form or as pure ore compounds. Selenium is present in metal sulfide ores, where it replaces sulfur to some extent. Selenium is produced commercially as a byproduct of the processing of these ores, most often during harvest.

Complete step by step answer:
Electronic Configuration of Selenium:
Since, the atomic number of Selenium is $34$. So, Selenium atoms have $34$ electrons in the ground state and the electronic shell structure is $\left[ {2,{\text{ }}8,{\text{ }}18,{\text{ }}6} \right]$.
So, electrons of the selenium atoms will be filled according to the diagonal rule and Aufbau principle.
According to the Aufbau principle, electrons occupy the lowest energy orbitals first, then the higher energy orbitals.
Diagonal rule – Electrons will be filled in these subshells according to the arrangement given below

where the maximum amount of electron each subshell can have is
$\ s \\\ p \\\ d \\\ f \\\ \$ $\ 2 \\\ 8 \\\ 18 \\\ 32 \\\ \$
According to the rules shown above, firstly $2$ electrons will be filled in $1s$subshell, then $2$ electrons will be filled in $2s$ subshell and so on.
So, the electronic configuration of Selenium atom in ground state is $1{s^2}{\text{ }}2{s^2}{\text{ }}2{p^6}{\text{ }}3{s^2}{\text{ }}3{p^6}{\text{ }}3{d^{10}}{\text{ }}4{s^2}{\text{ }}4{p^4}\;$

Note:
If the energy of an atom is increased, an electron in the atom gets excited and hence the number of electrons increases. To go back to its ground state, the electron releases energy, and the electrons gained for the excited state.