ABSTRACT
Helium is the first multi-electron atom, the first noble gas, and the first element with truly amazing properties. It is the first, and most noble, of the noble gasses. It has the highest first ionization potential of any element. It has a second ionization potential that is higher than one might expect, based just on the first ionization potential of hydrogen. People study liquid helium because it presents puzzles for our understanding of physics, especially in the area of thermodynamics. Liquid helium has two named sub-states, called helium I and helium II. Helium I is not very conspicuously different from ordinary helium gas, since it has low refraction, viscosity, and density, making its surface hard to notice. Helium II is the one with the interesting behavior: climbing container walls and such.
