Question

The atomic number of chlorine is 17. Its electronic configuration is:
(A) K, L, M = 2, 10, 5
(B) K, L, M = 2, 8, 7
(C) K, L, M = 7, 8, 2
(D) K, L, M = 5, 10, 2

Answer 1

Hint: Start by writing the electronic configuration of chlorine as we have been already given an atomic number of chlorine which is 17. Think about the chemistry learnt in lower classes and how we used to write the electronic configuration in shells and not orbitals. Accordingly modify the electronic configuration to get the answer.

Complete step by step solution:
- Chlorine is an element in the periodic table which belongs to the halogen family.
- Chlorine has the atomic number 17.
- It belongs to group 17 in the periodic table.
- The electronic configuration of chlorine is $1s^{2}2s^{2}2p^{6}3s^{2}3p^5$.
- Now, in the options, the electronic configuration is represented in terms of shells that is, K, L, M.
- We have learnt in lower classes that K-shell is the innermost shell and first shell around the nucleus of the atom.
- Similarly, L-shell is the second shell around the nucleus and M-shell is the third shell from the nucleus.
- To calculate the number of electrons in each shell we have the formula, $2N^2$ where N is the number of the atomic shell.
- So, for K-shell, the number of atomic shells, N is 1 and so, the total number of electrons is 2.
- Similarly, for L-shell, N=2 and total number of electrons is 8.
- Similarly, for M-shell, N=3 and total number of electrons is 18.
- Now, we just need to fill electrons of chlorine in the shells correctly to get the answer.
- So, for chlorine, K=2, L=8 and M=7 (2+8+7=17).
- Therefore, the electronic configuration of chlorine is K, L, M = 2, 8, 7 respectively.

- Therefore, the answer is option (B).

Note: K, L, M, N, and so on represent the number of shells in an atom. The maximum number of electrons which can be filled in each shell is given by the formula, $2N^2$ where N is the number of shells. K is the innermost shell and first shell around the nucleus which is followed by L-shell, M-shell, and so on.