The chemical symbol of hydrogen is H. It is an element with atomic number 1, this means that 1 proton is found in the nucleus of hydrogen.

Hydrogen is the lightest, simplest and most commonly found chemical element in the Universe, making up around 75% of its elemental mass.

Hydrogen is found in large amounts in giant gas planets and stars, it plays a key role in powering stars through fusion reactions.

Hydrogen is one of two important elements found in water (H₂O). Each molecule of water is made up of two hydrogen atoms bonded to one oxygen atom.

In 1766, during an acid metal reaction, Henry Cavendish first formally recognized hydrogen. In 1781 he also found that hydrogen produces water when burned. While Cavendish is usually given credit for the discovery of hydrogen as an element, it had been produced by earlier scientists who were unaware of hydrogen as a unique chemical element.

It wasn’t until a few years later (1783) that hydrogen was given its name. The word hydrogen comes from the Greek word hydro (meaning water) and genes (meaning creator).

Hydrogen gas has the molecular formula H₂. At room temperature and under standard pressure conditions, hydrogen is a gas that is tasteless, odorless and colorless.

Hydrogen can exist as a liquid under high pressure and an extremely low temperature of 20.28 kelvin (-252.87°C, -423.17 °F). Hydrogen is often stored in this way as liquid hydrogen takes up less space than hydrogen in its normal gas form. Liquid hydrogen is also used as a rocket fuel.

Under extreme compression hydrogen can also make a transition to a state known as metallic hydrogen. Laboratory research into this area is ongoing as scientists continue efforts to produce metallic hydrogen at low temperature and static compression.

Hydrogen is used to power a range of new alternate fuel vehicles. The chemical energy of hydrogen is converted by a combustion method similar to current engines or in a fuel cell which produces water and electricity by reacting hydrogen with oxygen.

Engineers and car manufacturers are researching the possibility of using hydrogen gas as an efficient and viable car fuel. One of the possibilities involves storing hydrogen as a solid state in car fuel tanks. While there are many challenges involved in this process it would allow for greater hydrogen storage in vehicles, allowing them to travel for longer before refueling.

Hydrogen peroxide is a chemical compound with the molecular formula H₂O₂. It is often used as a hair bleach or cleaner. At certain concentrations it can also be used to clean wounds.

Hydrogen was used for air travel from 1852 when the first hydrogen lifted airship was created by Henri Giffard. Later airships that used hydrogen were called zeppelins and while they were reliable and safe for the majority of the time their use was stopped soon after the Hindenburg disaster in 1937. The Hindenburg airship was destroyed in a midair fire over New Jersey that was both filmed and broadcast live on radio.

Hydrogen is commonly used in the petroleum and chemical industries and is also widely used for many physics and engineering applications such as welding or as a coolant.

Hydrogen can be potentially dangerous to humans due to fires that can start when it is mixed with air, our inability to breathe it in its pure oxygen free form and also in its extremely cold liquid state.