Md

Mendelevium

Identification

CAS Number: 7440-11-1

Discovery Year: 1955

Discoverer: G.T.Seaborg, S.G.Tompson, A.Ghiorso, K.Street Jr.

Discovery Location: United States

Properties

Atomic Mass: 258 →Density: 10.3 g/cm³ →

Atomic Dimensions

Van der Waals Radius: 246 pm

Thermodynamics

Melting Point: 1100 K →

Electronic Structure

Electron Config: [Rn] 5f13 7s2

Block: f

Period: 7 →

Oxidation States: +3

Abundance & Geochemistry

Goldschmidt Class: synthetic

About

Radioactive metallic transuranic element. Belongs to the actinoid series. Only known isotope, Md-256 has a half-life of 1.3 hours. First identified by Glenn T. Seaborg, Albert Ghiorso and associates in 1955. Alternative name Unnilunium has been proposed. Named after the 'inventor' of the periodic table, Dmitri Mendeleev.

Isotopes

Md-258 258 ☢ 51.5 d

Md-260 260 ☢ 27.8 d