Also, helium tends to escape the atmosphere into space! Air is just a ton of colliding molecules, and something like helium has an atomic mass of ~4, compared t

Also, helium tends to escape the atmosphere into space! Air is just a ton of colliding molecules, and something like helium has an atomic mass of ~4, compared to say nitrogen, which has an atomic mass of ~14, and it is in the N2 form, so it has a mass of ~18. So, an N2 molecule is way more massive than a helium atom. As a result, helium at the same temperature as nitrogen has a much higher average velocity and can escape the earth's gravity at a high rate.