Question

Why does potassium have 4 energy levels?

Answer 1

1. Bohr postulated that electrons revolve around the nucleus in a definite circular path called shell or orbit.
2. These shells are called energy levels.
3. These shells are denoted as K, L, M, N or numbers 1,2,3,4.
4. The maximum number of electrons in each energy level is given by the formula $2{\mathrm{n}}^2$ where $\text{'}\mathrm{n}\text{'}$is the energy level.
5. So, the maximum number of electrons in each shell is
   1st orbit, K-shell = $2\times {\left(1\right)}^2=2$ electrons.
   2nd orbit, L-shell = $2\times {\left(2\right)}^2=8$ electrons.
   3rd orbit, M-shell = $2\times {\left(3\right)}^2=18$ electrons.
   4th orbit, N-shell = $2\times {\left(4\right)}^2$ = $32$electrons.
6. Potassium has the atomic number 19 and has 19 electrons.
7. So, the number of electrons in each shell is as follows-
8. The K-shell will have $2$ electrons.
9. The L-shell will have $8$ electrons.
10. The M-shell will have $8$ electrons. This shell doesn't have nine electrons even though it can hold up to eighteen electrons due to the octet rule.
11. The octet rule states that the outermost valence shell must contain eight electrons to have a stable noble gas configuration.
12. M-shell if contains the nine electrons, will be the outermost valence shell which will make the element unstable. Thus, this electronic configuration is not possible.
13. M-shell contains eight electrons.
14. The N-shell will have the remaining $1$ electron.
15. Hence, potassium has four energy levels.