aftertrio.blogg.se

Under high pressure, however, helium can form various compounds, for example, helium-nitrogen clathrate (He(N 2) 11). Other compounds, known as Van der Waals compounds of helium are also formed with lithium and cryogenic helium gas. Helium can exist in molecular ion form, such as HeH +, which is a highly stable but reactive form of helium. In plasma form or subjected to electron bombardment, helium can from unstable compounds with certain metals including, sulfur, iodine, phosphorus and tungsten.

Helium is an inert (Nobel) gas under all standard conditions. Helium can solidify at higher temperature under high pressure. The refractive index of solid and liquid helium is almost the same and it is difficult to distinguish between the two states. Helium solidifies at -272C at a pressure of 2.5 MPa (25 bar). This occurs due to quantum mechanics as the zero-point energy of helium is significantly high and does not allow freezing. Helium remains in liquid form at absolute zero, at standard pressure. Helium is also highly affected by the magnetic field and interacts with Earth’s magnetosphere to from aurora. The plasma state of helium has high electrical conductivity. There is a considerable difference between the two states of helium. The atomic state of helium is predominant in the outer earth and space. Helium is present in plasma state on Earth. Helium is hardly soluble in water and is in fact, the least soluble monoatomic gas. Its boiling point is close to absolute zero. It has the lowest melting point among all elements. Russia and Qatar have also developed helium production plants. New reserves of helium have been discovered in North America. USA has been the biggest producer of helium since its discovery, but till 2012, most of the helium reserves have been exhausted and now account for 30% of the world’s helium supply. About 3000 metric tons of helium are produced annually in the lithosphere (the layer of Earth including upper mantle and the crust). The primary source of helium on Earth are minerals of thorium and uranium, which emit alpha particles (helium nuclei). Helium is the most abundant gas in the Earth’s heterosphere (the layer of atmosphere around 80km above Earth). There is a continuous production of helium on the Earth (via radioactive decay), but it readily escapes the Earth’s atmosphere and enter the space. The atmospheric content of helium on the Earth is only 5.2 ppm. However, it is the 2 nd most abundant element in the universe.

Helium was used as lifting gas for air craft in World War I and in World War II, helium was produced widely and used in welding of shielded arc and lifting gas. Helium was isolated by William Ramsay in 1895. These lines were named “Helium” by Norman Lockyer, from the word Helios, which is the name of Greek God of the Sun. In the solar eclipse of 1868, several scientists studied the spectral lines coming from the sun and observed the presence of distinct and unknown yellow lines. The discovery of helium is linked with its primary sources, the sun. It was discovered in 1868 by Jules Janssen and Norman Lockyer.

Helium is the second most abundant element in the universe and is primarily produced because of radioactive decay.