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Helium is the second lightest element(hydrogen's the first), with an atomic mass of 4.0026. It is used in helium baloons, blimps, zepelins, deep sea diving, low temperature experiments etc, to make high voices.... It was discovered by Sir William Ramsey in 1895. It's name comes from the Greek word helios which means sun.

At room temperature, helium is a colorless and odorless gas. It has 2 electrons and 2 protons. It is the only nonreactive element without eight electrons. The most common helium atom has 2 neutrons but it can have 3 or even 4. All isotopes are stable.

A helium atom. The most common helium atom has two neutrons, two protons, and two electrons.

Sir William Ramsey, the discoverer of helium.

Helium has one energy level with two electrons and has a hexagonal structure. It has a density (at 283 K) of 0.1785 grams per centimeter cubed.

Blimps like this one are filled with Helium.

Helium has the lowest melting point of any element, and its boiling point is close to absolute zero. Helium can never be a solid (unless you dramatically change the pressure). The heat of helium is very high. It is the 2nd most abundant element in the universe and is often found on very hot stars. Helium makes up about 23% of the mass of the universe. In fact, it was found on the sun before it was discovered on earth! It is very rare on earth. The earth's gravity isn't strong enough to trap a lot of helium. It does not conduct electricity(very very little). It doesn't react with air or fire. It is unreactive but has formed compounds with flourine. The sun is constantly producing helium.

The sun is constantly making helium