Americium
|
|
| General |
|---|
| Name, Symbol, Number
|
americium, Am, 95
|
| Chemical series
|
actinides
|
| Group, Period, Block
|
7, f
|
| Appearance
|
silvery white
|
| Atomic properties |
| Atomic weight
|
[243] amu
|
| Atomic radius (calc.)
|
175 pm (no data)
|
| Covalent radius
|
no data
|
| van der Waals radius
|
no data
|
| Electron configuration
|
[Rn]5f7 7s2
|
| e- 's per energy level
|
2,8,18,32,25,8,2
|
| Oxidation states (Oxide)
|
6,5,4,'''3''' (amphoteric)
|
| Physical properties |
| Density
|
13700 kg/m3
|
| State of matter
|
solid
|
| Melting point
|
1449 K (2149 °F)
|
| Boiling point
|
2880 K (4725 °F)
|
| Crystal structure
|
hexagonal
|
| Hardness
|
no data
|
| Magnetic ordering
|
no data
|
| Molar volume
|
17.63 ×10-6 m3/mol
|
| Heat of vaporization
|
no data
|
| Heat of fusion
|
14
.4 kJ/mol
|
| Vapor pressure
|
no data
|
| Velocity of sound
|
no data
|
| Miscellaneous |
| Electronegativity
|
1.3 (Pauling scale)
|
| Specific heat capacity
|
no data
|
| Electrical conductivity
|
2.2 106/m ohm
|
| Thermal conductivity
|
10 W/(m
|
| 1st ionization potential
|
578 kJ/mol
|
| Most stable isotopes |
| iso | NA | half-life | DM | DE MeV | DP
>- |
>241Am >>{syn.}
>432.2 y
>SF
α
5.638
|
237Np
|
| 242mAm
|
{syn.}
|
141 y
|
IT
α
SF
|
0.049
5.637
|
238Np
|
| 243Am
|
{syn.}
|
7370 y
|
SF
α
|
5.438
|
239Np
|
|
! colspan="2" bgcolor="#ff99cc" | SI units & STP are used except where noted.
Americium is a
synthetic element in the
periodic table that has the symbol Am and
atomic number 95. A radioactive
metallic element, americium is an
actinide that was obtained by bombarding
plutonium with
neutrons and was the fourth transuranic element to be discovered. It was named for the
Americas, by analogy with
europium.
Notable characteristics
Freshly prepared americium
metal has a white and silvery luster (more silvery than
plutonium or
neptunium) and at
room temperatures it slowly tarnishes in dry air. Alpha emission from Am-241 is approximately three times
radium.
Gram quantities of Am-241 emit intense
gamma rays which creates a serious exposure problem for anyone handling the element.
Applications
This element can be produced in
kilogram amounts and has some uses (mostly Am-241 since it is easier to produce relatively pure samples of this isotope). Americium has found its way into the household, where one type of
smoke detector contains a tiny amount of Am-241 as a source of
ionizing radiation. Am-241 has been used as a portable gamma ray source for use in
radiography. The element has also been employed to gauge
glass thickness to help create flat glass. Am-242 is a neutron emitter and has found uses in neutron radiography. However this isotope is extremely expensive to produce in usable quantities.
History
Americium was first synthesized by
Glenn T. Seaborg, Leon O. Morgan, Ralph A. James, and
Albert Ghiorso in late 1944 at the wartime Metallurgical Laboratory at the
University of Chicago (now known as
Argonne National Laboratory). The team created the
isotope Am-241 by subjecting
plutonium-239 to successive neutron capture reactions in a
nuclear reactor. This created Pu-240 and then Pu-241 which in turn decayed into Am-241 via
beta decay.
Isotopes
18 radioisotopes of americium have been characterized, with the most stable being Am-243 with a half-life of 7370 years and Am-241 with a half-life of 432.2 years. All of the remaining radioactive isotopes have half-lifes that are less than 51 hours, and the majority of these have half lifes that are less than 100 minutes. This element also has 8 meta states, with the most stable being Am-242m (t
½ 141 years). The isotopes of americium range in atomic weight from 231.046 atomic mass unit|amu (Am-231) to 249.078 amu (Am-249).
References
External links
Category:Chemical elements
Category:Actinides
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