Characteristics of hydrogen
Hydrogen is the chemical element of symbol H and atomic number 1. Its nucleus is formed of only a proton, orbited by one electron. This makes hydrogen to be the lightest of all elements, with an average atomic mass of 1.00784 amu.
This element is a colourless, odourless, tasteless, non-toxic, and it is a highly flammable gas. Once it has been ignited, it burns as a pale blue, almost invisible flame. In the moment of combustion, when hydrogen enters in contact with oxygen water is produced, being the only residue that is produced in the combustion of hydrogen. For example, the space shuttle of NASA used liquid hydrogen as fuel, and liquid oxygen as an oxidizer. What got out from the fuel tanks was so water vapour, as these two elements combine in the moment of combustion.
Abundance in the universe
Hydrogen is the most abundant chemical element in the universe. It represents the 75%, in mass, of all of the baryonic matter (the one we interact with). The stars are mainly composed of this element. In the central part of the latter, there is a fusion process between the hydrogen atoms, due to the high temperatures and the pressure it is subjected to. It is from this fusion process that stars get their energy.
However, it is very rare to find this element free, as it is combined with other compounds to form different substances. For example, it combines with oxygen to form water (H2O), or with carbon, to form hydrocarbons, like methane (CH4), butane (C4H10)… As it is the lightest substance of all, it is found in the outermost parts of the atmosphere, and it even escapes from the gravitational field of our planet. It is calculated that the Earth loses 3 kilograms of hydrogen every second, which over a year represents 95 000 tonnes of lost hydrogen.
The isotopes of hydrogen
The isotopes of a chemical element are atoms that in their nucleus have the same number of protons as the original element, but a different number of neutrons. So, the isotopes conserve the same characteristics of the original element, but with a different number of neutrons.
In particular, hydrogen has 3 types of natural isotopes, which are written 1H, 2H and 3H. However, this element has other isotopes, which are very unstable and have never in observed in nature, even if they have been synthesized in the laboratory. These isotopes that are so unstable go from the 4H to the 7H.
Hydrogen is the only element that has different names for its isotopes.
This isotope of hydrogen, known as deuterium (of symbol D), contains a proton and a neutron in its nucleus. Deuterium isn’t radioactive and doesn’t represent a significant toxicity threat. Water enriched with this isotope is named heavy water.
The 3H, known as tritium (of symbol T), contains a proton and two neutrons in its nucleus. Tritium is a radioactive isotope, and its period of semi-disintegration is of approximately 12.3 years. In the natural environment, small quantities of tritium are produced due to the interaction of cosmic rays with the gases of the atmosphere. The ITER, the most advanced fusion reactor in the world, pretends to fusion deuterium and tritium atoms to produce big quantities of energy.
The other isotopes of this element aren’t found in nature and have been created artificially in diverse ways. For example, in the case of the 4H, was created by bombarding tritium with nuclei of deuterium. This one and the hydrogen isotopes with more neutrons have a semi-disintegration period of about 10-23 seconds.
Hydrogen as fuel
Hydrogen is the fuel with the most energetic density: 1 kilogram contains the same energy as 2.8 kilograms of methane. Hydrogen could be used in the future to propel cars, as it is an energy with a non-existent environmental impact, as when it enters in combustion its unique residue is water. Moreover, it is very efficient as fuel. In a vehicle propelled by hydrogen, approximately 60% of the chemical energy of hydrogen is converted into mechanical energy for the vehicle, while the mechanical performance of the thermic motors, like the ones of petrol or diesel oil, is between a 20 and a 35%.
Furthermore, hydrogen is vastly used in the industry, and it is easy to store and transport. So, hydrogen could be used in the future as a very efficient and clean energy. Nowadays cars that work with this element are already being designed.