* They exist as individual atoms, not molecules. Helium is a noble gas, meaning its atoms are very stable and don't readily form chemical bonds with other atoms. This is why helium exists as single atoms in its gaseous state.

* They are very small and light. Helium has the smallest atomic radius and lowest atomic mass of all the elements. This contributes to its unique properties like low density and high diffusion rate.

* They are constantly moving and colliding. Like all gases, helium atoms are in constant random motion. They collide with each other and with the walls of their container, creating pressure.

* They are weakly interacting. Due to their full electron shells, helium atoms have very weak interatomic forces. This makes them behave like an ideal gas under many conditions.

* They can be excited to higher energy levels. While helium atoms are generally stable, they can absorb energy and become excited. This can lead to the emission of light, as seen in helium-neon lasers and the characteristic orange-yellow glow of helium gas discharge.

In summary: Helium gas consists of individual, small, and light atoms that are constantly moving and weakly interacting. These properties give helium unique characteristics, making it useful in applications ranging from balloons to scientific research.