Hydrogen

Hydrogen is the most abundant of all the elements, and has the chemical symbol H and an atomic number of 1. Despite this abundance, naturally occurring elemental hydrogen is extremely rare on Earth.

Hydrogen
Properties
Atomic symbol	H
Atomic number	1
Classification	Gas
Atomic mass	1.001 amu
Other Information

Isotopes

The most common form of hydrogen is protium, although this name is rarely used and it is generally known simply as hydrogen. Protium atoms consist of a single proton orbited by a single electron. Two other hydrogen isotopes are known to exist: deuterium, which has one neutron and an atomic weight of 2, and tritium with two neutrons and an atomic weight of 3. Tritium is radioactive, with a half-life of 12.32 years. Naturally occurring tritium is extremely rare on Earth but has a number of valuable applications, such as light-emitting inserts for optical instruments and emergency equipment. As a result it is extremely expensive.

Compounds

Hydrogen can be found in the vast majority of organic compounds, as well as many inorganic compounds. It is an important component of water and most acids.

Fuel for vehicles

Hydrogen is one of two fuels needed for fuel cells (the other being oxygen), which have the potential to be a major form of alternative energy in the future. Fuel cells are very clean energy sources; their only by-products are water and heat. Since no pollutants or greenhouse gases are produced, the use of fuel cells could provide cleaner air and potentially slow down global warming.

Unfortunately, hydrogen is not a viable fuel source at present. Today's average car, for example, would require an unfeasibly large fuel tank to carry enough hydrogen for practical purposes. Hydrogen is also extremely flammable and suitable safeguards are needed to reduce the chances of a fatal explosion in an accident. There is also the issue of obtaining the pure hydrogen needed. Hydrogen can be obtained from distilled water through electrolysis, but this requires the same amount of energy the Hydrogen's use in a fuel cell would yield. Fuel cells would not solve the eventual energy crisis; it would simply move the problem to the power plants providing the energy to obtain the hydrogen through electrolysis.

If hydrogen could be used in cars, it would be important in establishing the hydrogen economy.

As free hydrogen does not exist on Earth, hydrogen is not actually a source of energy but rather a carrier of it: its value as a fuel is that it provides a clean and efficient way to use energy produced by some other source. Due to the Second Law of thermodynamics the energy used to produce hydrogen must be at least equal to the energy contained within it, meaning that at present it is not a viable fuel for most applications. Potential solutions include the use of bacteria that produce hydrogen through photosynthesis, which would effectively allow solar energy to be stored in hydrogen and used as fuel.