ElementsWhat are the noble gases?
The noble gases fill the last column of the table. Their atoms have a full outer shell of electrons, so they have almost no tendency to react with anything. All are gases without colour or smell. They are present in air in small amounts and are collected by cooling air until it turns liquid. They glow with bright colours when electricity passes through them, which is how neon signs work.
The family in numbers
Melting points in this family run from -272.2 °C (helium) to -71.1 °C (radon). The most recently discovered member is oganesson (2006).
Why they do not react
Atoms react in order to reach a full outer shell of electrons. The noble gases already have one, so they have nothing to gain. They do not even pair up with each other: where oxygen and nitrogen go about as two-atom molecules, a noble gas is made of single atoms. For a long time they were called the inert gases and thought to form no compounds at all. In 1962 the first compound of xenon was made, and a few compounds of xenon and krypton are now known, though helium and neon still have none in ordinary conditions.
Where you meet them
Helium is the second most abundant element in the universe but scarce on Earth. It is lighter than air and does not burn, so it fills weather balloons and party balloons, and as a liquid it is the coldest coolant there is, used around the magnets of MRI scanners. Argon is the most plentiful noble gas in the air, close to one percent of it. It fills ordinary light bulbs and shields hot metal from the air during welding. Neon gives the orange-red glow of neon signs, and xenon the bright white light of some car headlamps and camera flashes.
Radon
Radon is different from the rest: it is radioactive. It forms in rocks and soil as uranium breaks down, and can collect in badly ventilated cellars and mines.
All noble gases compared
| No. | Symbol | Name | Atomic mass | State | Melts at | Boils at | Density g/cm³ | Discovered |
|---|---|---|---|---|---|---|---|---|
| 2 | He | Helium | 4.00260 | Gas | -272.2 °C | -268.9 °C | 0.0001785 | 1868 |
| 10 | Ne | Neon | 20.180 | Gas | -248.6 °C | -246.1 °C | 0.0008999 | 1898 |
| 18 | Ar | Argon | 39.9 | Gas | -189.3 °C | -185.8 °C | 0.0017837 | 1894 |
| 36 | Kr | Krypton | 83.80 | Gas | -157.4 °C | -153.2 °C | 0.003733 | 1898 |
| 54 | Xe | Xenon | 131.29 | Gas | -111.8 °C | -108.1 °C | 0.005887 | 1898 |
| 86 | Rn | Radon | 222.01758 | Gas | -71.1 °C | -61.7 °C | 0.00973 | 1900 |
| 118 | Og | Oganesson | 295.216 | Gas | no value | no value | no value | 2006 |
Other families: alkali metals, alkaline earth metals, transition metals, post-transition metals, metalloids, nonmetals, halogens, lanthanides, actinides.