Why does helium react

frequency very rare

After hydrogen atoms, helium atoms are the second most common in the universe with a share of around nine percent. In the sun, the element is created through the fusion of hydrogen atoms. In the earth's envelope, helium occurs only with a small mass fraction of 0.0000004%. This comparatively small number is due to the low mass of the helium atoms and the lack of helium compounds. The average helium concentration in the air is around five ppm. The noble gas is found in large quantities as a radioactive decay product in natural gas and oil.


Partial solar eclipse
The French astronomer Jules Janssen traveled to India for the total solar eclipse in 1868.
In the solar spectrum he observed a new spectral line that indicated a new element.
   

Helium atoms of the isotope He-4 have two protons, two electrons and two neutrons. The natural helium consists of a mixture of two different isotopes. With a share of 0.00014%, the isotope He-3, which has only one neutron per atom, is relatively rare. Certain radioactive substances, the alpha emitters, emit particles that consist of helium nuclei. These are twice positively charged, they are missing two electrons.


Share of noble gases in the air in percent by volume
 
argon0,9340
neon0,001818
helium0,0005240
krypton0,000114
xenon0,0000087
radon6 × 10−18
 
Argon is the most common noble gas in the air, followed by neon and helium. Lit [5]