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Meave60
May 21, 2015

Atomic radius generally decreases from left to right across a period. The radius of a positive ion is generally smaller than the neutral atom due to the reduction in the shielding effect, resulting in the positively charged nucleus attracting the remaining electrons more strongly.

Since the elements listed are in the same period, #"Ca"# would be expected to have the larger radius because it is in group 2. #"Ga"# is in group 13, #"Ga"^(3+)# would be smaller than #"Ga"#, and #"Br"# is in group 17.

http://en.wikipedia.org/wiki/Ionic_radius

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