Question

Write the electronic configuration of the following of the following element:

${}_{17}{}^{35}\mathrm{Cl}$

Answer 1

Electronic configuration: It is the distribution of electrons in the various energy levels or orbits or shells around the nucleus of an atom.

Step-1: Find out the total number of electrons in the species

In Chlorine (Cl), ${}_{17}{}^{35}\mathrm{Cl}$

As for any element X, atomic number and mass number is written as ${}_{\mathrm{Atomic}\mathrm{number}}{}^{\mathrm{Mass}\mathrm{number}}\mathrm{X}$

• Therefore, for Chlorine, Atomic number = 17
• Also, Atomic number = Number of protons
• So, number of protons = 17
• Since an atom is electrically neutral, therefore the number of protons= number of electrons
• Therefore, number of electrons = 17

Step-2: Follow the Bohr-Bury scheme to write an electronic configuration

1. Distribute the electrons from shell 1 or shell K onwards, such as 1, 2, 3….etc. or K,L, M ……etc.
2. Fill the shell upto its maximum capacity and then move to the next shell. Maximum capacity of a shell is counted from the formula 2n² where n= 1 for shell 1 (or K) , 2 for shell 2 (or L) and so on.
3. Maximum number of electrons in valence shell is 8.

Shell	Maximum capacity	Electrons added
K	2	2
L	8	8
M	18	7

Here 7 electrons are added to M shell because only 17 electrons need to be distributed. As 2+ 8+ 7 makes a total of 17, stop after 17 electrons are distributed.

So the electronic configuration of ${}_{17}{}^{35}\mathrm{Cl}$ in K, L and M shell is 2, 8, 7 respectively.