Question

If K and L shells of an atom are full, then what will be the total number of electrons in the atom?
a.) 12
b.) 8
c.) 10
d.) 16

Answer 1

Hint: The problem is talking about KLMN… method is based on electron shells, with the labels KLMN…. K denotes the first shell (or energy level), L denotes the second shell, M, the third shell , and so on.

Step by step solution:
The names of the electron shells come from a fellow named Charles G. Barkla, a spectroscopist who studied the X- rays that are emitted by atoms when they are hit with high energy electrons. And the innermost shell is now called the K-shell, after the label used for the X-ray.
K is the lowest energy and can only be occupied by two electrons, then L shell by 8 electrons and the M shell by 18.
The maximum number of electrons in a shell can be calculated By Bohr bury scheme, According to which number of maximum electrons in a shell = \[2{{n}^{2}}\], where ‘n’ is shell number.
So, for K-shell:
 n = 1;
Maximum number of electrons = \[2{{(1)}^{2}}\]=2
For, L-shell:
n = 2;
Maximum number of electrons = \[2{{(2)}^{2}}\]=8
When both shells are completely filled then:
Total number of electrons in the atom = 2+8 = 10
And it has zero valency.
So, the answer is “C”.

Note: These shells are also called orbits. And the K-shell electrons are closest to the nucleus. Energy level increases from K-shell to L-shell and so on.