Helium has two valence electrons. As an element, helium is very stable and contains a single s-orbital on its outer shell.
Helium is the periodic table's least reactive element, and it sits at the top of the noble gas group. In addition to being monoatomic, it has a low boiling point and is the second most common gas in the universe. It is small, light and does not react with any other elements. Helium has the following characteristics:
- It is colorless
- It is a gas at room temperature
- It has a density of 0.0002 g/cm^3
- Its boiling point is 4.2 K
- Its heat vaporization point is 0.1 kJ/mol
- Its thermal conductivity is 0.15 j/m sec K
- It is a natural gas
Helium's electron configuration is 1s^2. It has seven isotopes, and two of them are liquid. Its electron affinity is 0 kJ/mol and it has an atomic radius of 31 pm.
Natural gas deposits contain 10 percent helium, which makes them an excellent resource for extracting it. People extracting helium can obtain it from sources in Russia, Texas, Poland, Algeria, China and Canada. When liquefied, it can be used to freeze biological materials for later use. In addition, scuba divers use air that is a blend of helium and oxygen for underwater breathing. Finally, people can use helium in balloons to make them float.