Mendelevium
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Mendelevium (pronounced men-deh-LEE-vi-em) is an artificially produced, radioactive element with the symbol Md and the atomic number 101. A metallic, radioactive, transuranic element of the actinides, mendelevium is synthesized by bombarding einsteinium with alpha particles. This element was named after Dmitri Mendeleev, who devised one form of the Periodic Table.
| Previous Element: Fermium Mendelevium Next Element: Nobelium |
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| 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 | |
| Abundance | ||
| 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 (PEL) | No limits | |
| OSHA PEL Vacated 1989 | No limits | |
| NIOSH Recommended Exposure Limit (REL) | No limits | |
| Sources: University of Wisconsin General Chemistry Mineral Information Institute Jefferson Accelerator Laboratory EnvironmentalChemistry.com | ||
Characteristics
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.
History
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.
Isotopes
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
- Los Alamos National Laboratory - Mendelevium lanl.org. 2003. Accessed on-line: 9/21/2009
- Steve Gagnon. It's Elemental - Mendelevium. Jefferson Lab. 2009. Accessed on-line: 9/21/2009
- Mark Winter. Mendelevium - WebElements.com. 1993 - 2009. Accessed on-line: 9/21/2009
- Kenneth Burbalace. Periodic Table of Elements - Mendelevium - Md. EnvironmentalChemistry.com. 1995 - 2009. Accessed on-line: 9/21/2009
- National Nuclear Data Center. NuDat 2.5. 2009. Accessed on-line: 9/17/2009
- The New Encyclopedia Britannica. 15th Edition, 2007. Volume 8. pp 5.
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