Chemical Principles seventh edition by Atkins, Jones, and Laverman. M H E Freeman presented by Macmillan Learning. Francium, Fr , is thought to be the most reactive of the group 1 alkali metals. However, it is radioactive, has a half-life on the order of minutes, and is available in only small amounts, making it difficult to study. Based on the properties of the other group 1 alkali metals and the periodic trends of these properties, predict the atomic radius, ionic radius of the 1 cation, and the first ionization energy of francium. Element Atomic radius (pm) Radius of 1 ion (pm) First ionization energy (kJ/mol) K 227 138 418 Rb 248 152 402 Cs 265 167 376 atomic radius of Fr : pm ionic radius of Fr : pm first ionization energy of Fr : kJ/mol