What are the chemical properties of helium gas?

When we look at the atomic structure of helium, we see an atom with a pair of protons in its nucleus (along with some neutrons), and a pair of electrons in orbit around it. What is probably most noteworthy is that the two electrons actually fill that electron shell, which is its valence shell, and this makes helium very resistant to the formation of chemical bonds with any other atoms. You'll recall that the essence of chemical bonds is basically the loaning and borrowing of electrons by atoms, or the sharing of electrons by atoms. Helium is "happpy" with its configuration, and it isn't interested in loaning, borrowing or sharing electrons. This makes helium inert; it's a noble gas of the Group 18 elements.

The chemical properties of helium are those properties where we investigate the bonds that helium makes with other atoms, either those like itself, or those different. Under any "normal" circumstances, helium won't bond with other atoms. Only in an "energized" or "excited" state will helium form compounds with another atom, and these compounds are uniformly unstable; they won't exist under anything close to "normal" conditions. If we excite helium with high voltage, we can get it to form compounds with elements like fluorine, iodine, phosphrus, sulfur and tungsten. But there aren't really a lot of chemical properties to any inert or noble gas. And that includes neon, argon, krypton, xenon and radon, which are the other Group 18 elements and have full outer (valence) electron shells.