Periodic Table


July 14, 2012, 1:56 am

Mendelevium (pronounced men-deh-LEE-vi-em) is an artificially produced, radioactive element with the symbol Md and the atomic number 101. Mendelevium is a metallic, radioactive, transuranic element of the actinides. The actinides are the elements located in the bottom row of the periodic table, having atomic numbers 89 through 103. A transuranic element is one that has a higher atomic number than uranium, these are man made and not found in nature. Mendelevium is synthesized by bombarding einsteinium with helium ions. This element was named after Dmitri Mendeleev, who devised one form of the Periodic Table.

caption Dmitri Mendeleev (Source: Berkeley Lab News Center)
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Next Element: Nobelium


Physical Properties
Color ---
Phase at Room Temp. ---
Density (g/cm3) ---
Hardness (Mohs) ---
Melting Point (K) 1100K
Boiling Point (K) ---
Heat of Fusion (kJ/mol) ---
Heat of Vaporization (kJ/mol) ---
Heat of Atomization (kJ/mol) ---
Thermal Conductivity (J/m sec K) ---
Electrical Conductivity (1/mohm cm) ---
Source Synthetic
Atomic Properties
Electron Configuration [Rn]7s25f13
Number of Isotopes 19 (0 natural)
Electron Affinity (kJ/mol) ---
First Ionization Energy (kJ/mol) 635
Second Ionization Energy (kJ/mol) ---
Third Ionization Energy (kJ/mol) ---
Electronegativity 1.3
Polarizability (Å3) 18.2
Atomic Weight 256.1
Atomic Volume (cm3/mol) ---
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) ---
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) ---
Ionic Radius3+ (pm) ---
Common Oxidation Numbers +3
Other Oxid. Numbers +2
In Earth's Crust (mg/kg) ---
In Earth's Ocean (mg/L) ---
In Human Body (%) ---
Regulatory / Health
CAS Number 7440-11-1
OSHA Permissible Exposure Limit No limits
OSHA PEL Vacated 1989 No limits
NIOSH Recommended Exposure Limit No limits
Mineral Information Institute
Jefferson Accelerator Laboratory



Researchers have shown that mendelevium has a moderately stable dipositive (II) oxidation state in addition to the more characteristic (for actinide elements) tripositive (III) oxidation state. The isotope 256Md has been used to find out some of the chemical properties of mendelevium, but it has no other uses outside of basic scientific research. Only trace amounts of the element have ever been produced. All isotopes of mendelevium that have been discovered are radioactive. Other isotopes range from 245 to 262 mass numbers, and have half-lives from a few seconds to about 51.5 days. The original 256Md had a half-life of 77 minutes. It is assumed that mendelevium’s standard state is solid at 298K, and its classification is metallic.


Mendelevium was first produced by Albert Ghiorso, Glenn T. Seaborg, Gregory R. Choppin, Bernard G. Harvey, and Stanley G. Thompson in 1955 at the University of California, Berkeley. The team produced 256Md when they bombarded an 253Es target with alpha particles (helium nuclei) in the Berkeley Radiation Laboratory’s 60-inch cyclotron (256Md was the first element to be synthesized one-atom-at-a-time). Element 101 was the ninth transuranic element synthesized. The first 17 atoms of this element were created and analyzed using the ion-exchange adsorption-elution method.


Fourteen isotopes of mendelevium have been characterized, with the most stable being 258Md with a half-life of 51.5 days, 260Md with a half-life of 31.8 days, and 257Md with a half-life of 5.52 hours. All of the remaining radioactive isotopes have half-lives that are less than 97 minutes, and the majority of these have half-lives that are less than 5 minutes. The isotope 258Md undergoes two different forms of radioactive decay, causing it to have two different half-lives, one of 57 minutes and one of 51.5 days.

Further Reading


Note: This article uses some material from the Wikipedia article Mendelevium that was accessed on August 25, 2009. The Author(s) and Topic Editor(s) associated with this article may have significantly modified the content with original content and with content drawn from other sources. All content has been reviewed and approved by those Author(s) and Topic Editor(s), and is subject to the same peer review process as other content in the EoE. The current version of the article differs from the version that existed on the date of access. This article is licensed under the GNU Free Documentation License 1.2. See the EoE’s Policy on the Use of Content from content partners and other sources for more information.



Coon, M. (2012). Mendelevium. Retrieved from


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