How does the atomic size vary as we go down a group?



Atomic size mainly depends on two factors.

• Effective nuclear charge

• Number of shells/orbits


In a group of periodic table effective nuclear charge has almost same value. But on going down the group every time a new shell is introduced. For example Helium has only K shell, Neon has K and L shell and so on.


Since effective nuclear charge doesn't much vary, but one extra shell is introduced down the group, thats why size of atoms increases when we go down the group.


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