| Name | Symbol | Atomic Number | Electronic Structure | Melting Point (°C) | Boiling Point (°C) |
|---|---|---|---|---|---|
| Helium | He | 2 | 2 | -272.20 | -268.93 |
It is the second most abundant element in the universe, making up about 20% of all atoms. Like Hydrogen, Helium was created during the Big Bang. All other elements have been synthesised inside stars by the nuclear reactions that give stars their energy.
The Helium atom consists of two protons surrounded by two electrons. Its Atomic Number is therefore 2. In the nucleus of Helium are two more particles that are neutral, neutrons.
The Helium nucleus is a very stable entity. The two electrons "orbiting" the nucleaus are also a very stable arrangement. Helium has little tendency to change or to react with other atoms. Helium forms no chemical compounds whatsoever. It is chemically inert. It is the lightest of the Noble Gases, substances with little or no chemical activity.
Helium atoms do not even join together with each other very easily. Because of this Helium can be cooled to a temperature of -269°C before the atoms come together enough for it to liquefy. Helium has the lowest boiling point of any liquid (just 4 degrees above Absolute Zero). At a temperature of -271 degrees C, liquid Helium changes into another form and begins to act very strangely. It loses all mechanical resistance: the liquid can migrate along the surface of a beaker so that it leaves its container!
Although Helium is the second most abundant element in the universe, it is rare on the Earth. Its light atom is not easily held by the Earth's gravity. Because it doesn't form compounds, it cannot link up with other atoms to become heavy enough to be held on the Earth, like Hydrogen does. The only reason it is found on Earth is that it is constantly being produced. When heavy atoms like Uranium break down (we say they are radioactive), their heavy nuclei throw out Helium nuclei. Helium is a product of radioactive decay.
Interestingly, it was first discovered, not on our world, but on the Sun.
When white light is passed through a prism, it is broken down into a spectrum, the colours of the rainbow. If this is done to sunlight, the spectrum is found to be crossed by dark lines. These lines are due to atoms in the sun's gaseous atmosphere absorbing certain wavelengths of the light. Each different type of atom absorbs different wavelengths. In other words, elements leave their fingerprints in the spectrum.
When the Sun's spectrum was first examined during the 1860s, most of the lines on the sun could be identified with elements known on the Earth. However, one series of lines could not be. Scientists postulated a new element to explain these lines and gave it the name of the Greek god of the Sun, Helios. By the turn of the century, Helium was located in rocks on the Earth.
The biggest uses of Helium are in deep sea diving (it lowers the risk of the bends) and for research into very low temperatures.
Hydrogen and Helium together account for 99% of all the atoms in the Universe. The outer gas giant planets and the Sun are mainly Hydrogen and Helium, reflecting these abundances. The Earth is too small to hold much of these substances. The Earth is made up mainly of the heavier elements, the remaining 1% of the atoms in the Universe. This might seem like a small amount of material but 1% of the Sun is enough material to make up 3,000 globes like the Earth. Read more about The Electromagnetic Spectrum and the information it can yield.
