What trend in atomic radius do you see as you go across a period/row on the periodic table. What causes this trend?

1 Answer
Mar 10, 2016

I think you clearly know that atomic radii DECREASE across a Period reading from left to right. Why??


Two factors are in opposition: (i) nuclear charge; and (ii) shielding by other electrons. Since nuclear charge #Z# increases sequentially across a Period, atomic radii should decrease sequentially. And so in fact they do. You will have to search out the data on atomic radii (and you should do this).

Thus, when electrons are added to the same valence shell, they tend to shield each other (i.e. by electron-electron repulsion) VERY imperfectly. So the effect of nuclear charge wins, and atomic radii decrease.

On the other hand, once the valence shell is full, electronic shielding of the nuclear core becomes more effective. The next valence shell is further removed from the nucleus, and the whole shooting match of shielding versus nuclear charge begins again.