Hydrogen is highly flammable and combines readily with oxygen to form water. When hydrogen is mixed with air it forms an explosive mixture that ignites with a single spark. It is such a powerful fuel that the main engines of the space shuttle are fuelled by hydrogen.
| Symbol: | H |
| Atomic number: | 1 |
| Relative atomic mass: | 1 |
| Electronic configuration: | 1s1 |
| Molecular formula: | H2 |
| Relative molecular mass: | 2 |
| Boiling point: | -253 °C |
| Key properties: | Low density and highly flammable, reducing agent. |
| Some major uses: | Feedstock for chemical production, fuel for fuel cells and rocket engines, removing oxygen during glass making. |
| Discoverer: | Henry Cavendish (1766) |
All around us
Hydrogen is the most abundant element in the universe. About 93% of all the atoms in the universe are hydrogen atoms. But it is the lightest element, so it forms about 76% of the mass of the universe. Hydrogen is also the most abundant element in the Sun but it only forms 0.14% of the Earth's crust. Water is a compound of hydrogen and oxygen. Water is the most abundant compound on the Earth's surface and covers about two-thirds of it.
The atmosphere only contains a tiny proportion of hydrogen gas, about 1 part per million (0.0001%). However, air contains much more water vapour. In very humid places the air can contain about 6% water vapour, while in a desert it might contain as little as 0.1% water vapour. Industry gets most of its hydrogen from natural gas or steam.
