Question

Chlorine is represented by the Lewis structure (image). The atomic number of an atom that give an identical electron dot-arrangement as shown above:
$$:\underset{..}{\overset{..}{Cl}}.$$
A.$11$
B.$9$
C.$7$
D.$19$

Answer 1

Hint: Lewis structure is an electron dot representation that shows the bonding between the molecules and the lone pairs that may exist in the molecule. A Lewis structure can be drawn for any covalent or coordinate molecule.

Complete step by step answer:
First we will read about Lewis structure and then we will see which compounds have identical dot-arrangements.
Lewis structure: Lewis structure is an electron dot representation that shows the bonding between the molecules and the lone pairs that may exist in the molecule. A Lewis structure can be drawn for any covalent or coordinate molecule. Lewis structure is drawn as: first take the atomic number and do the electronic configuration. And then the number of electrons present in the outer most orbit will be shown in the Lewis structure.
How to draw Lewis structure: First write the atomic symbol of the element at the centre and then put the dots equal to the number electrons present in the outer-most orbit. For example: if we have made Lewis structure for the hydrogen atom then it will follow the following steps: (i) the electronic configuration of the atomic number of hydrogen i.e. $1$ is $1s$.(ii) So it has one electron in its outer most orbit. So representation will be as: $H\circ$. Similarly can be done for other atoms.
Now, in this question we have to find the atom which has the same dot-arrangement as that of chlorine atom. The atoms which have the same number of electrons in their outermost orbit will show the same dot-representation. Here we are given with the atomic numbers as $11,9,7$ and $19$. If we write the electronic configuration for each atom then we will get as: $1s^{2}2s^{2}2p^{6}3s^1$ for atomic number $11$, $1s^{2}2s^{2}2p^5$ for atomic number $9$, $1s^{2}2s^{2}2p^3$ for atomic number $7$ and $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^1$ for atomic number $19$. And we know that for chlorine atoms the atomic number is $17$ hence it’s electronic configuration is as $1s^{2}2s^{2}2p^{6}3s^{2}3p^5$. Hence it is clear that the number of electrons in the outermost orbit is the same as that of chlorine is in an atom which has an atomic number as $9$.
So option B is correct.

Note:
Lewis structures, also known as Lewis dot diagrams, Lewis dot formulas, Lewis dot structures, electron dot structures, or Lewis electron dot structures, are the diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.