Helium is pure. Rare gas is a mixture because it contains helium, atmosphere, argon and other substances.
Helium is a rare gas. The name of this element comes from Greek, which means "the sun". 1868, French Zhan Sen observed the surface of the sun with a spectroscope and found a new yellow spectral line, which he thought belonged to an unknown element on the sun, hence the name helium.
Helium is a colorless and odorless gas under normal circumstances, and it is the only substance that cannot be solidified under standard atmospheric pressure. Helium is the most inactive element. Helium is mainly used as protective gas, working fluid of gas-cooled nuclear reactor and ultra-low temperature refrigerant. In addition, helium can also be used as a floating gas because its density is lower than that of air and its properties are stable.
On February 6th, 2065438+July, Wang He and Zhou Xiangfeng of Nankai University in China and their collaborators published a report on the sodium helium compound-Na? He's paper ends the history that helium has no compounds, which indicates that China has moved to the forefront in the field of rare gas chemistry.
Content distribution
Helium exists in the whole universe, accounting for 23% of the mass, second only to hydrogen. But it mainly exists in natural gas or radioactive ore. In the earth's atmosphere, the concentration of helium is very low, only one in fifty-two thousand. Helium contained in radioactive minerals on earth is the product of alpha decay.
Helium in some natural gas is economically worth extracting, up to 7%. The helium content in American natural gas is about 1%. Helium in surface air is 4.6 cubic centimeters per cubic meter, accounting for about 0.0005% of the whole volume, and its density is only 7.2 times that of air. It is the least dense gas except hydrogen.