Page 12 - Curriculum Visions Dynamic Book

Helium (He)
Element 2. Helium is an inert (unreactive), colourless, and odourless gas in group 8 (the noble gases) in the Periodic Table. It is the second most abundant element, the second lightest (after hydrogen) in the universe and is very common in the hotter stars.
Helium is too light to be common in our atmosphere, although it is found combined with natural gas. Helium
is obtained by liquefying natural gas. The helium is the last component
to liquefy. Helium never becomes a solid under ordinary air pressure.
Very cold helium (below –270.8°C)
is sometimes called the fourth
state of matter because it behaves
so oddly. For example, it suddenly changes from being an insulator to a superconductor of electricity.
Discovery
Helium was discovered by the French astronomer Pierre Janssen in 1868 as a yellow line when looking at the light given out by the Sun.That is how the element got its name.
Technology
Helium is used in balloons and as an inert gas when there would otherwise be a risk of explosion with the lighter gas hydrogen. It is put into gas cylinders for divers, used to inflate some aircraft tyres, and to provide an inert atmosphere for delicate laboratory experiments, such as for growing crystals.
Geology
The helium that occurs on the Earth is a result of radioactive decay. It is normally isolated from natural gas mixtures, where concentrations can be as high as 7%.
Biology
Helium is less soluble in blood than nitrogen is and comes out of the blood more easily than nitrogen. It is
Key facts...
Name: helium
Symbol: He
Atomic number: 2
Atomic weight: 4.00
Position in Periodic Table: group 8 (18)
(noble gases); period 1
State at room temperature: gas Colour: colourless
Density of gas at 20°C: 0.117 g/cc Melting point: none (at atmospheric
pressure); –272°C (only under pressure) Boiling point: –269°C
Origin of name: named from the Greek helios,
meaning the Sun
Shell pattern of electrons: 2
For more on helium, see Volume 1: Hydrogen and the Noble Gases in the Elements set.
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