Comparison of Selenium and Rubidium

Attribute	Selenium ×	Rubidium ×
Atomic mass (u)	78.97	85.468
Standard state	Solid	Solid
Oxidation states	-2 +4 +6	+1
Electron configuration	[Ar]4s²3d¹⁰4p⁴	[Kr]5s¹
Atomic radius (van der waals) (pm)	190	303
Electronegativity (pauling scale)	2.55	0.82
Electron affinity (eV)	2.021	0.468
Ionization energy (eV)	9.752	4.177
Boiling point (K)	958	961
Melting point (K)	493.65	312.46
Density (g/cm³)	4.809	1.53
Atomic number	34	37
Group name	Nonmetal	Alkali metal
Discovered (year)	1817	1861
Symbol	Se	Rb