Helium is an element that has the atomic number 2 and is a gaseous substance. The chemical symbol for helium is He. The electron configuration of helium is 1s2. The atomic symbol of helium is 42He. An atom of helium is composed of 2 protons and 2 neutrons in the nucleus along with 2 electrons in its 1s orbital. Therefore, the atomic mass of helium is 4.002602 amu. At room temperature and pressure, helium is a colorless and odorless gas. Helium is considered as the second most abundant element in the universe. It exists as a monoatomic gas.
The melting point of helium is about -272.2oC, which is a very low value. The boiling point of helium is given as -268oC. This makes it a gas for a wider range of temperatures. In the periodic table of elements, helium is categorized as an s block element but is placed in the right side corner of the table. This is because helium is an inert gas that will not undergo chemical reactions. It is also a non-metal.
Since helium is a noble gas, it only shows zero oxidation state. There are two known isotopes of helium. They are 3He isotope and 4He isotope. 4He is the most abundant form among them and its abundance is given as 99%. Both of these isotopes are stable and no radioactive decay can be observed. However, there are some other isotopes as well. They are unstable and radioactive.
Helium is widely used in balloons. In addition, helium is used to provide a controlled atmosphere for many synthesis reactions (such as synthesis of silicon crystals) due to its high inertness. It is also used as an inert shield for arc welding. Helium can be converted to its liquid form, which is known as liquid helium and is used as an important cryogenic material.