Question

How many core electrons are present $_{19}K$?

Answer 1

The electrons in an atom that are not valence electrons and do not participate in chemical bonding are known as Core electrons.

Complete step by step solution:
-The atomic core consists of the nucleus and the core electrons of an atom.
-Core electrons are held strongly bound to the nucleus. Therefore, unlike valence electrons, core electrons are important and play a secondary role in chemical bonding and reactions by screening the positive charge of the atomic nucleus from the valence electrons.
-The electrons present in the s and p outermost subshell orbitals are called the valence electrons.
-Valence electrons are responsible for interaction between atoms and the formation of chemical bonds
-So, as the find the number of core electrons of $_{19}K$, we need to write the electronic configuration first,
Electronic configuration of potassium in ground state = $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}4{{s}^{1}}$
Valence electrons present = 1 (which is present in the s-orbital)
-Number of core electrons = Total number of electrons – Valence electrons = 19 – 1 = 18

Note: What is the difference between valence electrons and core electrons? The outermost electrons present in an atom are called valence electrons, whereas the innermost electrons present in an atom are called core electrons. Electrons are filled in an atomic orbital following the Hund’s rule and Aufbau principle. Electrons occupying space in inner electron shells are called Core electrons, whereas the electrons which occupy the outermost electronic shells are called Valence electrons. The more the number of inner electrons, the more is the shielding effect.