Group 2A of the Periodic table contains the Alkaline Earth metals. Those elements are Beryllium ( Be ), Magnesium ( Mg ), Calcium ( Ca ), Strontium ( Sr ), Barium ( Ba ) and Radium ( Ra ). Beryllium is the lightest member of the group 2A. Ionic radius increases moving down the group and decreases from left to right across the period of elements. In the group 2A, the ionic radius increases from Beryllium ( 59 pm - picometers ) to Radium ( 163 pm ). Answer: Beryllium has the lowest ionic radius.