HELIUM (He)
Helium is a noble gas, it is the second-least reactive noble gas (after neon). The name helium comes from the Greek word helios, which means the sun. Helium is commercially the most important of the noble gases. It is used as a coolant to perform experiments at a very low temperature. Helium has the lowest boiling point of any known substance (-269 °C), so liquid helium is the coldest liquid refrigerant available. As we have seen, hydrogen is the simplest atom with only one proton and one electron. Helium is composed of two electrons bound, to a nucleus containing two protons along with either one or two neutrons. While hydrogen is 7% more buoyant than helium it has a much higher fire risk. Helium is the second-most abundant element in the universe, though it is much less common on Earth. It is colorless, odorless, tasteless, non-toxic, and inert. Most helium is obtained by extracting it from natural gas. In fact, all natural gas contains at least trace quantities of helium. Helium is monatomic under standard conditions. Inhaling helium temporarily changes the sound of a person's voice. Though helium is non-toxic, breathing it can result in asphyxiation due to oxygen deprivation. Evidence of helium's existence came from observation of a yellow spectral line from the sun. Helium’s mass is 0.1786 g/L
A mixture of helium and oxygen is used as an artificial atmosphere for divers and others working under pressure. Helium is used for filling balloons and blimps.