Periodic trends for cations and anions

[aardvarkm12]

I understand that for electronegativity, it increases going right and going up. For atomic radius, it increases going left and going down. BUT...what about cations and anions for electronegativity and atomic radius? How do you figure out those problems?

For example: which of the following has the largest size? K+, Mg2+, Ca2+, or Sr2+?

For example, which of the following is most electronegative? K+, Mg2+, Ca2+, or Sr2+?

Thanks in advance!

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[Alucard6]

For atomic radius, if you have a positive charge then you are SMALLER than neutral size. This is because you lose an outer shell electron and in most cases you will completely lose your valance shell and thus become much smaller.

So for the question: Mg, Ca and Sr are all +2, so Sr would be the biggest of those three since it increases going down. Now you compare K+ and Sr2+. Both cases you lose the outer shell, but Sr2+ is still bigger since it is a period lower and has 1 extra valence shell than potassium.

For electornegativity, I am not 100% but I think you would relate it to the atomic radius. A SMALLER atomic radius = LARGER electronegativity because a smaller bond means the atoms can be closer together and the atom can receive an electron more readily (more electronegative).

So for the problem: Mg2+ should be the smallest and thus most electronegative.

As an FYI, there is a Study Question sub-area you can post in for better responses.