Question

How many electrons are in the highest occupied energy level of a neutral chlorine atom$?$

Answer 1

Hint: At first find out the atomic number of the chlorine atom and write the electronic configuration of a chlorine atom. Since it is neutral no gain or loss of electrons occurs and the number of electrons remains the same. Then use the Bohr model to find out the number of electrons present in the highest occupied energy level.

Complete step-by-step answer:
Now, according to the atomic model proposed by Niels Bohr first energy level of an atom takes up two electrons, second energy level takes up eight electrons, third energy level takes eighteen electrons and so on.

Now, the atomic number of chlorine is $17$. We know the atomic number of an element or atom is equal to the number of protons present in the nucleus of the atom. In order to maintain the neutrality of the atom the number of electrons present in the atom is also equal to the atomic number. Hence the number of electrons present in the chlorine atom is $17$.

So the electronic configuration of chlorine atoms is $\left[ {Ne} \right]3{s^2}3{p^5}$. Since we are considering a neutral chlorine atom no gain or loss of electrons occurs from the atom and hence the electron count remains same so does the electronic configuration. From the electronic configuration we can see the valence shell consists of the highest energy $s$ and $p$ subshells.

Since the $s$ subshell contains two electrons and the $p$ subshell contains five electrons. The total number of electrons present in the highest occupied energy level of a neutral chlorine atom is seven.

Note: For this type of question you should know the periodic table properly. If you know the periodic table then you can easily know the atomic number of a given element and hence find its electron count which is the most important step in the given question.