Comparison of Potassium and Rubidium

Attribute	Rubidium ×	Potassium ×
Atomic mass (u)	85.468	39.0983
Standard state	Solid	Solid
Oxidation states	+1	+1
Electron configuration	[Kr]5s¹	[Ar]4s¹
Atomic radius (van der waals) (pm)	303	275
Electronegativity (pauling scale)	0.82	0.82
Electron affinity (eV)	0.468	0.501
Ionization energy (eV)	4.177	4.341
Boiling point (K)	961	1032
Melting point (K)	312.46	336.53
Density (g/cm³)	1.53	0.89
Atomic number	37	19
Group name	Alkali metal	Alkali metal
Discovered (year)	1861	1807
Symbol	Rb	K