Research Elements Ra · atomic number 88 Alkaline earth metal · period 7, group 2 [Rn] 7s2 Shells: 2, 8, 18, 32, 18, 8, 2 Valence electrons: 2 in the outer shell (7s2) Green dots are the outer shell's s and p electrons. Softer green dots are the d electrons of transition metals, and the d and f electrons of lanthanides and actinides: they often take part in bonding, but not always. Grey dots are the core. Ground-state configuration from the NIST Atomic Spectra Database (A. Kramida, Yu. Ralchenko, J. Reader and the NIST ASD Team). No natural isotope with a defined abundance in NIST's Atomic Weights and Isotopic Compositions.Radium
Electrons
Natural isotopes