Group 1 (IA, Alkali Metals)ElementAtomic Number (Z)Symbolrubidium37Rbcesium55Csfrancium87FrFirst ionization energy decreases as you go down Group 1 because the electron being removed is further from the nucleus (in a higher energy level).3 more rows read more
Transition Metals; Alkali Metals; Noble Gases; Alkaline Earth Metals; Halogens; 7) Sulfur has a first ionization energy of 999.6 kJ/mol. Rubidium has a first ionization energy of 403 kJ/mol. read more