Helium has monatomic molecules, and is the lightest of all gases except hydrogen. . Helium, like the other noble gases, is chemically inert. Its single electron shell is filled, making possible reactions with other elements extremely difficult and the resulting compounds quite unstable. Helium is the most difficult of all gases to liquefy and is impossible to solidify at normal atmospheric pressures. These properties make liquid helium extremely useful as a refrigerant and for experimental work in producing and measuring temperatures close to absolute zero. Liquid helium can be cooled almost to absolute zero at normal pressure by rapid removal of the vapor above the liquid. At a temperature slightly above absolute zero, it is transformed into helium II, also called superfluid helium, a liquid with unique physical properties. It has no freezing point, and its viscosity is apparently zero; it passes readily through minute cracks and pores and will even creep up the sides and over the lip of a container. Helium-3, the lighter helium isotope of mass 3, which has an even lower boiling point than ordinary helium, exhibits markedly different properties when liquefied.
    Because it is noncombustible, helium is preferred to hydrogen as the lifting gas in lighter-than-air balloons; it has 92 percent of the lifting power of hydrogen, although it weighs twice as much. Helium is used to pressurize and stiffen the structure of rockets before takeoff and to pressurize the tanks of liquid hydrogen or other fuel in order to force fuel into the rocket engines. It is useful for this application because it remains a gas even at the low temperature of liquid hydrogen. A potential use of helium is as a heat-transfer medium in nuclear reactors because it remains chemically inert and nonradioactive under the conditions that exist within the reactors.
THINK ABOUT HELIUM'S CHEMICAL INERTNESS IN TERMS OF ITS HAVING ITS FIRST PRINCIPAL ENERGY LEVEL OR SHELL FILLED.  DOES THIS ELEMENT NEED TO TAKE OR DONATE ELECTRONS?