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Identification
Hydrogen is the smallest and lightest atom. Though it can exist in various "heavy" forms by adding neutrons, the most common form of hydrogen has only one proton and one electron, making it extremely simple. It is also the most abundant element in the universe and makes up 75% of the universe's mass. Pure hydrogen gas is rare on the earth and is commonly produced industrially from hydrocarbons, where the majority of the gas is immediately used. Most of the the universe's hydrogen occurs in its plasma form in stars.
Misconceptions
For many people, the term hydrogen ion exists in terms of acid-base chemistry. A hydrogen cation is typically referred to as a proton, as it consists solely as a proton with no electrons, which has major implications in the Bronsted theory of acids, which refers to an acid as a proton donor and a base as an electron acceptor. This terminology for a hydrogen ion, however, can be misleading, as a naked proton does not exist in any sort of solution due to its tendencies to bind to other molecules. As a result, in solutions involving water, a hydrogen ion is often referred to as a hydronium ion, which is the addition of a proton to a water molecule.
Types
A more stable form of a hydrogen ion is known as the dihydronium ion, which consists of two protons and one electron. As such, it is the simplest possible molecule and can be found primarily in interstellar space. Dihydrogen cations can be formed in two ways: the reaction of a trihydrogen cation with a high energy photon or an electron. In both cases, an additional electron is formed. Dihydrogen cations can react to form trihydrogen cations, and trihydrogen cations can react with dihydrogen cations as well, although in the latter case there is no net change of materials, even though changes in the subatomic spins can result.
Types
The trihydrogen cation was first observed in 1911 from the analysis of plasma discharges. During this analysis, a unique molecule with a 3:1 mass-to-charge ratio was identified, which was postulated to be either the trihydrogen cation or a carbon with no electrons. Since the latter is highly unlikely, as well as the fact that this specie was observed to increase when additional hydrogen gas was added, it was concluded that the unidentified molecule was a trihydrogen cations. Trihydrogen cations are difficult to analyze because they have no dipole moment (a measurement of the relative electron affinity within a molecule, dipole moments are nonexistent in trihydrogen cations because all three atoms are equidistant and have the same affinity for electrons). Examination via ultraviolet light is also impossible due to the fact that it would destroy the molecule. Finally, via the use of a technique called Rovibronic spectroscopy allowed for the identification and analysis of the trihydrogen cation. It is able to stably exist in space due to low temperatures and the low density of interstellar space, and was found to primarily exist in the atmospheres of such Jovian planets as Jupiter, Saturn, and Uranus, as well as in the plasma region of stars.
Significance
The hydrogen ion, due to its simplicity, has a central role in the understanding of chemistry and subatomic physics. An ionized hydrogen atom is central to the Bronsted theory of acids. In addition, the dihydrogen cation is often used as a textbook example for solving the Schrodinger equation for a molecule; since it has only one electron, the electron-electron repulsion calculations can be ignored. Finally, the trihydrogen cation, which takes the form of an equilateral triangle, is often used of an example for the calculation of electron orbitals over an entire molecule. These unique features of the hydrogen ion, as well as its abundance in stars, planetary atmospheres, and other regions where the physical state of plasma can occur, make it an interesting and important feature in many different areas of science.