Helium

Helium(He)

Atomic mass:4.0026 u

Melting point:-272.2°C (0.95 K)

Boiling point:-268.93°C (4.22 K)

SOLID STATE

Helium is the only element that cannot be solidified by sufficient cooling at normal atmospheric pressure; it is necessary to apply pressure of 25 atmospheres at a temperature of 1 K (−272 °C, or −458 °F) to convert it to its solid form.

LIQUID STATE

Liquid helium may show super fluidity. Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 k Pa). At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temperature of −269 °C (−452.20 °F; 4.15 K).

USES

In more recent decades, liquid helium has been used as a cryogenic refrigerant (which is used in cryocoolers), and liquid helium is produced commercially for use in superconducting magnets such as those used in magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR), Magneto encephalography (MEG), and experiments in physics, such as low temperature Mössbauer spectroscopy.

GASEOUS STATE

Helium is a colourless, odourless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling and melting point are the lowest among all the elements.

USES

Helium is used as an inert-gas atmosphere for welding metals such as aluminium; in rocket propulsion (to pressurise fuel tanks, especially those for liquid hydrogen, because only helium is still a gas at liquid-hydrogen temperature); in meteorology (as a lifting gas for instrument-carrying balloons); in cryogenics (as a coolant because liquid helium is the coldest substance); and in high-pressure breathing operations (mixed with oxygen, as in scuba diving and caisson work, especially because of its low solubility in the bloodstream). Meteorites and rocks have been analysed for helium content as a means of dating.