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Atomic Number	68

Atomic Symbol	Er

Atomic Weight	167.26 amu

Group	Rare Earth (Lanthanide Series)

Form	Solid

Density @ STP	9.07 g/cm³

Melting Point	1529 °C (2784.2 °F, 1802.15 °K)

Boiling Point	2868 °C (5194.4 °F, 3141.15 °K)

Heat of Fusion	19.9 kJ/mol

Heat of Vaporization	285 kJ/mol

First Ionization Potential	6.1078 eV

Electronegativity (on Pauling scale	1.24

Specific Heat Capacity	0.168 J/g K

Ground State Electron Configuration	4f¹² 5s² 5p⁶ 6s²

Oxidation State(s)	+3

Stable Isotopes and Natural Abundance on Earth	¹⁶²Er, 0.14%; ¹⁶⁴Er, 1.61%; ¹⁶⁶Er, 33.6%; ¹⁶⁷Er, 22.95%; ¹⁶⁸Er, 26.8%; ¹⁷⁰Er, 14.9%

Atomic Radius	226 pm

Crystal Structure	Hexagonal

Discovered by	Mosander, 1842