Why does Mg2+ have the ionic radii bigger than Ca2+

If they were atoms, $\ce{Mg}$ should have a smaller radii. How does this change?

• Can you point to a source that says calcium ion is smaller than magnesium ion? – Brinn Belyea Feb 16 '15 at 3:59
• An exercise book.Also look here: answers.yahoo.com/question/index?qid=20071216145936AAgZZnv "To answer your question: (out of Ca2+ and Mg2+ )Mg2+ is larger because it they are cations and Mg is above Ca;" – user13411 Feb 16 '15 at 4:08

Ca2+ is bigger than Mg2+

as shown in the above pic Mg2+has more smaller size then Ca2+... I'm sorry but your question is wrong, Why Ca2+ has bigger Ionic Radii then Mg2+? because

No of Shells increases down the group

-Property of Periodic table

therefore ->

As you move down a group in the periodic table , additional layers of electrons are being added, which naturally causes the ionic radius to increase as you move down the periodic table.