Because there is only one electron shell in the outermost layer of helium atom, which contains two electrons, it is only a stable electronic configuration, so it is not easy to form compounds or valence elements, but exists in the form of a single atom. In this way, the particles that make up helium are actually helium atoms.

The force between helium particles is van der Waals force, which is essentially equivalent to intermolecular interaction, but different from the chemical bond interaction between atoms in compounds or simple molecules. Therefore, from the nature of the interaction force, we can think that these helium atoms have the nature of molecules (specifically monoatomic molecules), so there is the saying of helium molecules. So it is correct to say that helium is composed of helium molecules and helium atoms, but we look at the problem from different angles.