Helium, English name helium, symbol He, colorless, odorless and nonflammable. The content of helium in the air is about 5.2 parts per million. Chemically inactive, usually not combined with other elements or compounds. 1July 908 10, Dutch physicist anis liquefied helium for the first time.
1868, French astronomer Janssen p j c (1824-1907) observed a yellow line d on the solar spectrum when observing the total solar eclipse, which is different from the two lines D 1 and D2 of the sodium spectrum that have long been known. At the same time, the British astronomer lockyer J N (1836-1920) also observed this yellow line D. At that time, astronomers thought that this line only existed in the sun and that it was also a metal element. So Locar named this element helium, which was spelled by two words. The root of helio comes from Greek? λιο? , meaning the sun god, and the suffix -ium refers to the metal element, namely "helium" (helium is called "helium" when it appears in the form of simple substance).
1895, Ramsey cooperated with another British chemist, travers (Travers M W, 1872- 196 1). When pitchblende is treated with sulfuric acid, an inert gas is produced, which is identified as helium by spectrum, confirming that helium is also a rare gas, and this gas also exists on the earth.
Helium is a colorless and odorless gas at room temperature and atmospheric pressure. Its volume content in air is 5.24× 10-6. It is the substance with the lowest critical temperature found by human beings. Dark yellow when discharged at low voltage.
Because helium travels almost three times as fast as air, people who inhale helium will speak more frequently. This interesting phenomenon makes people who inhale helium speak in a shrill voice, just like cartoon characters in the old days.
Helium is a monoatomic molecule, which is chemically inactive. Helium generally does not produce compounds, but it can form helium ions, helium hydride plasma and molecules when excited in a low-voltage discharge tube. Helium ions are also called alpha particles.
The density of helium gas is much less than that of air (the density of air is 1.29kg/m3, and the density of helium gas is 0. 1.786kg/m3), which is extremely inert and safer than hydrogen gas (hydrogen gas can burn in air and may cause explosion). Helium is often used as inflation gas for spacecraft or advertising balloons.
Helium is often used as a shielding gas for welding magnesium, zirconium, aluminum, titanium and other metals due to its inert chemical properties.
The vowel letter e is pronounced with the long vowel /i/ in stressed syllables. When pronouncing, the end of the tongue is close to the lower teeth, and the front of the tongue is raised very high, but it does not touch the upper jaw and does not rub. Gums together, lips flat, appear at the beginning, middle or end of words, such as:
He ta
We, we ...
Me, me.
Yes, yes.
Even even
Mimi
Fever, fever.
Zebra zebra
I hope it can help you solve the problem.