Atomic Radius Question

Which element has the largest atomic radius: Br, K, Mg, or Na....please dont just answer please explain why i want to learn!! thanks

Well, atomic radius increases from right to left and top to bottom. This is the opposite of the electronegativity trend as you may have noticed. As electronegativity decreases, atomic radius increases, because the electrons are less attracted to the nucleus and maintain a greater distance from it. Shielding also plays a part, because although Na is in the same group as K, Na has less shielding because it has fewer electron shells. This means what few electrons it has are more strongly attracted to its nucleus, and are much closer to it.

That being said, K has the largest atomic radius of those listed. It is the least electronegative of each given choice and therefore its electrons are less attracted to the nucleus.

Look at the periodic table. Whichever one has the highest mass has the larger atomic radius. It's common sense.