Question

Relarionship between atomic radius and ionisation enthalpy

Answer 1

Ionization energy is the energy required by an neutral gaseous atom to remove an electron from its valence shell, hence turning itself into a cation. So, if ionisation energy is low, the atom would have a tendency to easily lose an electron and turn into a cation.  

In a period : It is common knowledge that as we go from left to right across a period, the atomic number increases. Basically, the number of electrons in the valence shell increase as we go from left to right. Now imagine a sodium and a chlorine atom. There is one electron in the valence shell of sodium (2,8,1) and seven electrons in the valence shell of chlorine(2,8,7). Positive and negative charges attract each other so the attraction between the nucleus and one electron of sodium will be quite low so the atomic radius will be high. On the other hand, the seven electrons of chlorine will be attracted greatly towards the nucleus making the atomic radius quite small.

Now, what do you think is easier: removing an electron which is loosely bound ( sodium) or removing an electron that is heavily bound (chlorine)? The answer is obviously that its easier to remove an electron from the sodium atom. If you notice, the sodium atom is in the left of period 3 and chlorine is in the right of period 3. Thus, as atomic number increases in a period, the energy required to remove an electron also increases, thus ionisation potential also increases on going left to right across the periodic table.

In a group : As we go down a group number of shells increases which inturn increase the atomic size. As I've said before, increase in atomic size means it will be less attracted towards nucleus, thus it will possess low ionisation energy as compared to the element above it.

As long as you remember than ionisation energy is inversely proportional to atomic size, you will have no problems.

Answer 2

Hyy here is your answer-


Lonization energy is the energy required by an neutral gaseous atom to remove an electron from its valence shell, hence turning itself into a cation. ... Positive and negative charges attract each other so the attraction between the nucleus and one electron of sodium will be quite low so theatomic radius will be high.

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