Atomic radius

[mokamia00]

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I keep on reading about atomic radius and i still cannot get it. If Na is smaller than K, why is K+ larger than Na+ ? Thanks

 

[SweetBurger]

As you go down a group in the periodic table the atomic radius will increase. This holds true for K+ and Na+. K+ is further down the table and therefore has more electrons which cause electron shielding which limits force of attraction from the protons in the nucleus which in turn allows K+ to have a larger atomic radius then that of Na+. Say you wanted to compare the atomic radius of K to K+. Then K+ would have a smaller atomic radius than K. This is true because you are removing an electron from the K in K+ therefore there is effectively less electron shielding on the furthest electrons allowing for the force of attractions from the protons in the nucleus to hold electrons closer. This effectively decreases the atomic radius.
Hope this clarifies and doesn't confuse.

 

[Quinoline]

Na is smaller than K and Na+ is smaller than K+ because of how many electron shells surround the nucleus. K and K+ have an addition set of s and p electrons that Na and Na+ don't have, which increases the size.