It is not always easy to make sensible comparisons between the elements however as some bonds are quite short because of multiple bonding (for instance the O=O distance in O2 is short because of the the double bond connecting the two atoms.

There are several other ways ways to define radius for atoms and ions. Follow the appropriate hyperlinks for literature references and definitions of each type of radius. All values of radii are given in picometres (pm). Conversion factors are:

1 pm = 1 x 10-12 metre (meter)
100 pm = 1 Ångstrom
1000 pm = 1 nanometre (nm, nanometer)
Neutral radii

The size of neutral atoms depends upon the way in which the measurement is made and the environment.

Follow the appropriate hyperlinks for definitions of each radius type. The term "atomic radius" is not particularly helpful although its use is widespread. The problem is its meaning,
Be(II) 31

which is clearly very different in different sources and books. Two values are given here, one is based upon calculations and the other upon observation - follow the appropriate link for further details.

Atomic radius (empirical): 105 pm

Atomic radius (calculated): 112 pm

Covalent radius (2008 values): 96 pm

Molecular single bond covalent radii: 102 (coordination number 2) pm

Molecular double bond covalent radii: 90 pm

Molecular triple bond covalent radii: 85 pm

Covalent radius (empirical): 90 pm

van der Waals radius: no information pm

Beryllium ( /bəˈrɪliəm/ bə-RIL-ee-əm) is the chemical element with the symbol Be and atomic number 4.

A divalent element, beryllium occurs naturally only in combination with other elements in minerals.

Notable gemstones which contain beryllium include beryl (aquamarine, emerald) and chrysoberyl.

The free element is a steel-gray, strong, lightweight and brittle alkaline earth metal.

It is primarily used as a hardening agent in alloys, notably beryllium copper.

Structurally, high flexural rigidity, thermal stability and thermal conductivity as well as low density (1.85 times that of water) make beryllium a superior aerospace material for high-speed aircraft, missiles, space vehicles and communication satellites.

Because of its low density and atomic mass, beryllium is relatively transparent to X-rays and other forms of ionizing radiation, and therefore is the most common window material for X-ray equipment and in particle physics experiments.

Commercial use of beryllium metal presents technical challenges due to the toxicity (especially by inhalation) of beryllium-containing dusts.

Beryllium produces a direct corrosive effect to tissue, and can cause a chronic life-threatening allergic disease called berylliosis in susceptible persons..

Because it is not synthesized in stars, beryllium is a relatively rare element in both the Earth and the universe.

The element is not known to be necessary or useful for either plant or animal life

Contents [hide]

1 Characteristics

1.1 Physical properties

1.2 Nuclear properties

1.3 Isotopes and nucleosynthesis

1.4 Occurrence

2 Production

3 Chemical properties

4 History

4.1 Etymology

5 Applications

5.1 Radiation windows

5.2 Mechanical applications

5.2.1 Mirrors

5.3 Magnetic applications

5.4 Nuclear applications

5.5 Acoustics

5.6 Electronic

6 Toxicity

7 See also

8 References

9 Further reading

10 External links

Characteristics

[edit]Physical properties

Beryllium has exceptional flexural rigidity (Young's modulus 287 GPa) and a reasonably high melting point.

The modulus of elasticity of beryllium is approximately 50% greater than that of steel.

The combination of this modulus and a relatively low density results in an unusually fast sound conduction speed in beryllium – about 12.9 km/s at ambient conditions.

Other significant properties are high specific heat (1925 J·kg−1·K−1) and thermal conductivity (216 W·m−1·K−1), which make beryllium the metal with the best heat dissipation characteristics per unit weight.

In combination with the relatively low coefficient of linear thermal expansion (11.4×10−6 K−1), these characteristics result in a unique stability under conditions of thermal loading.[3]

[edit]Nuclear properties

Beryllium has a large scattering cross section for high-energy neutrons, thus effectively slowing the neutrons to the thermal energy range where the cross section is low (about 0.008 barn).

The predominant beryllium isotope 9Be also undergoes a (n,2n) neutron reaction to 8Be, that is, beryllium is a neutron multiplier, releasing more neutrons than it absorbs.

This nuclear reaction is:

9

4Be + n → 2(4

2He) + 2n

Beryllium is also transparent to most wavelengths of X-rays and gamma rays, making it useful for the output windows of X-ray tubes and other such apparatus.

Also, beryllium is a good source for relatively-small numbers of free neutrons in the laboratory.

These are liberated when beryllium nuclei are struck by energetic alpha particles[3] producing this nuclear reaction:

4Be + 4

2He → 12

6C + n

where 4

2He is an alpha particle and 12

6C is a carbon-12 nucleus.[4]

[edit]Isotopes and nucleosynthesis

Main articles: Isotopes of beryllium and beryllium-10

Plot showing variations in solar activity, including variation in 10Be concentration.

Note that the beryllium scale is inverted, so increases on this scale indicate lower 10Be levels
9Be is the only stable isotope.

Thus, it is a monoisotopic element.

Cosmogenic 10Be is produced in the atmosphere of the Earth by the cosmic ray spallation of oxygen and nitrogen.

Cosmogenic 10Be accumulates at the soil surface, where its relatively long half-life (1.36 million years) permits a long residence time before decaying to boron-10.

Thus, 10Be and its daughter products are used to examine natural soil erosion, soil formation and the development of lateritic soils, as well as acting as a proxy for measurement of the variations in solar activity and the age of ice cores.

[5]
The production of 10Be is inversely proportional to solar activity, because the increased solar wind during periods of high solar magnetic activity in turn decreases the flux of galactic cosmic rays that reach the Earth.