Question

How does the atomic radius of argon compare to that of chlorine?

Answer 1

In order to answer this question, we should know about the effective nuclear charge of the chlorine and argon atoms. First, we should know about the location of chlorine and argon in the periodic table.

Complete answer:
We know that there is greater attraction from the nucleus in case of argon because as the electrons increase, effective nuclear charge also increases.
Let us completely understand the explanation why the atomic radius of argon is less than that of chlorine.
According to the periodic table, chlorine is located in group $17$ whereas argon is located in group $18$ . We know that relative atomic radius is mostly determined by how many electron shells are there and by the number of protons that are in a nucleus.
When we go down the group (the columns) of the periodic table. The atomic radius will increase because the elements at the bottom will have more energy level than the elements above it. The electrons of the elements at the bottom are farther away from the nucleus.
Also, when we go left to right on the periodic table, the atomic radius will decrease. This happens because no shells are being added since all the electrons in that period are present in the same shell. When we go left to right, we add an electron and proton. As the proton has higher attraction than the electron, the proton will win over the electron –electron repulsion between the outer electron shell and other shell, it will shrink the outer shell. This will mean that adding a proton and electron will decrease the atomic radius.
As argon is to the right of the chlorine and on the same period. Therefore, argon has an atomic radius less than chlorine’s atomic radius.

Note:
Remember the periodic trend of the periodic table i.e. when we go down the group, atomic radius will increase whereas when we go left to right, atomic radius will decrease. Also, remember the location of the elements in the periodic table.