What is the atomic mass of helium?

Helium has an atomic mass of 4.00 atomic mass units. The gaseous element also has an atomic number of 2 and an atomic symbol of He. Its atomic number correlates with the number of protons and electrons the element has, while the element's neutrons can be determined from its mass.

Helium has exactly two protons and two electrons; it has an atomic number of 2. It also has two neutrons, as its atomic mass minus its atomic number equals two. The element is classified as a noble gas and is found in group 18 on the periodic table. It is an inert atom because it has eight valence electrons and is completely stable.