The periodic table/Helium atom

From Wikiversity
< The periodic table(Redirected from Helium atom)
Jump to: navigation, search
Nuvola apps edu science.svg Subject classification: this is a chemistry resource .
Tulliana launch.png Completion status: this resource is just getting off the ground. Please feel welcome to help!
38254-new folder-12.svg Resource type: this resource is an article.

Helium (He) is the second element of the periodic table. It exists almost solely as a gas, and is very unreactive. It belongs to a group of elements on the periodic table known as noble gases.

Discovery[edit]

Pierre-Jules-César Janssen, a French astronomer, noticed a yellow line in the sun's spectrum while studying a total solar eclipse in 1868. Sir Norman Lockyer, an English astronomer, knew it could not be produced by any element known at the time. It was hypothesized that a new element on the sun was responsible for this yellow emission. This unknown element was named helium by Lockyer.

Helium was found on earth in 1895. Sir William Ramsay, a Scottish chemist, conducted an experiment with a mineral containing uranium called clevite. He exposed the clevite to mineral acids and collected the gases that were produced. He then sent a sample of these gases to two scientists, Lockyer and Sir William Crookes, who were able to identify the helium within it. Two Swedish chemists, Nils Langlet and Per Theodor Cleve, independently found helium in clevite at about the same time as Ramsay.

Occurrence[edit]

Universal[edit]

Helium consists of 24% of the elemental mass of the Milky Way (our galaxy). Helium is the second most abundant element in the universe (after Hydrogen).

Terrestrial[edit]

In the Earth's atmosphere, the concentration of helium by volume is only 5.2 parts per million. However, helium is found in large amounts in uranium, thorium, clevite, and pitchblende.

Quick Facts[edit]

Symbol: He

Atomic Mass: 4.002602

Classification: group 0 (noble gases)

Protons: 2

Electrons: 2

Neutrons: 2

Colour: colourless

Discovery in: 1895

Density: 0.1786 g/L

Crystal Structure: hexagonal

Melting Point: -272 °C (1 K)

Boiling Point: -268 °C (5 K)

Common Uses: artificial atmospheres, laser media, refrigerants, helium balloons, deep-sea diving, helium tanks, helium/neon lasers

See Also[edit]