Question

What is the electron configuration using core notation for \[S{{e}^{2-}}~\]?

Answer 1

Hint: We know that 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.

Complete step-by-step answer:
Selenium is a chemical element that is placed in the \[16th\] group and \[4\text{ }th\] period in the periodic table. The symbol of the selenium element is Se. It is a nonmetal element with the atomic number \[34.\] It shows similar properties as sulfur, tellurium, and arsenic. Sulfur is placed above selenium and tellurium is placed below selenium in the \[16\text{ }th\]group of the periodic table. Arsenic is found at the left of selenium in the\[~4th\] period and \[15\text{ }th\] group.

As it is found in the \[16th\] group so, it is a p – block element. Due to its various properties sometimes, it is considered as a metalloid as well. Selenium was discovered and isolated by Swedish Chemists Jons Jacob Berzelius and Johann Gottlieb Gahn in \[1817.\]The word selenium is derived from the Greek word ‘selene’ which means moon. It is rarely found as pure ore or in pure elemental form.

The atomic No. of \[Se\] is \[~34\] , \[S{{e}^{2-}}~\]has \[34+2=36\] electrons
Electronic configuration of $Se$ in Normal Notation: \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{10}}4{{s}^{2}}4{{p}^{4}}\]

Electronic configuration of \[S{{e}^{2-}}~\] in Normal Notation: \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}3{{d}^{10}}4{{s}^{2}}4{{p}^{6}}\]
In core notation it is Krypton core i.e. \[\left[ Kr \right].\]

Note: Remember that 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. 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.