The periodic table of the elements is a graphic display of the 118 described chemical elements geometrically organized by selected properties of their atomic structures. Elements are set forth by increasing atomic number]], the number of protons in the atomic nucleus.
While rectangular in general outline, gaps are included in the horizontal rows in order to keep elements with similar properties together in vertical columns (termed groups); examples of these groups are noble gases, alkali metals, alkali earths and halogens.
Uranium is a radioactive element that occurs naturally in low concentrations (a few parts per million) in soil, rock, and surface and groundwater. It is the heaviest naturally...
UraniumLast Updated on 2013-12-15 23:42:25Uranium is a radioactive element that occurs naturally in low concentrations (a few parts per million) in soil, rock, and surface and groundwater. It is the heaviest naturally occurring element, with an atomic number of 92. Uranium in its pure form is a silver-colored heavy metal that is nearly twice as dense as lead and is pyrophoric when finely divided.
Uranium exhibits three crystallographic modifications as follows: alpha --(688°C)→ beta --(776°C)→ gamma. It is a little softer than steel, and is attacked by cold water in a finely divided state. It is malleable, ductile, and slightly paramagnetic. In air, the metal becomes coated with a layer of oxide. Acids dissolve the metal, but it is unaffected by alkalis.
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National Institute of Standards and TechnologyLast Updated on 2012-01-21 00:00:00
The National Institute of Standards and Technology (NIST) is a United States federal agency within the U.S. Department of Commerce.
The institute was founded in 1901 with the aim of advancing measurement science, standards, and technology. NIST was known between 1901–1988 as the National Bureau of Standards (NBS).
NIST has an operating budget of about $1,600,000,000 and operates in two locations: Gaithersburg, Maryland and Boulder, Colorado. NIST employs a staff of about 2,900 scientists, engineers, technicians, and support and administrative personnel. About 2,600 associates and facility users from academia, industry and other government agencies complement the staff.
Article 1, Section 8 of the United States Constitution grants the U.S. Congress the power to "To coin money, regulate the value thereof, and of foreign coin, and fix... More »
AstatineLast Updated on 2010-06-05 00:00:00
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Next Element: Radon
Phase at Room Temp.
Melting Point (K)
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)
Synthetic (Th or U... More »
Argon-39Last Updated on 2010-03-29 00:00:00
Argon-39 is an isotope of argon that is useful as a tracer in ocean studies. It is a radioactive inert gas with a half life of 269 years and is produced in the atmosphere by cosmic ray interacting with Argon-40.
This article is written at a definitional level only. Authors wishing to expand this entry are inivited to expand the present treatment, which additions will be peer reviewed prior to publication of any expansion.
This argon isotope is well-mixed through the troposphere and its variation in concentration over the last 1000 years has been estimated to be no more than about seven percent. This means that its distribution in the atmosphere and ocean is in steady state.
It enters the ocean by gas exchange with the equilibrium time between the surface mixed layer and the atmosphere being about a month. The equilibrium concentration in surface... More »
MendeleviumLast Updated on 2009-11-24 21:05:57
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.
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