The ionization energy for hydrogen is 1312 kilojoules per mole. This is the same as the ionization potential and is the energy required to remove one electron from the atom. While other elements have more than one ionization energy, representing the energy to remove subsequent electrons, an atom of hydrogen has only one electron for removal. Ionization energy measures the ability of the atom to participate in chemical reactions.
Hydrogen, with atomic number one, is the simplest of all atoms. Electrically neutral atoms include a single proton and electron held together. However, on earth hydrogen rarely exists in the monatomic state. The hydrogen atom combines with a second hydrogen atom, forming elemental hydrogen gas or with another elemental atom to form compounds.
The bond between the atoms of diatomic hydrogen is extremely difficult to break. It has an enthalpy of 435.88 kilojoules per mole at 25 degrees Celsius. Increasing the temperature to 2,730 degrees Celsius increases the disassociation of this bond to 7.85 percent. However, monatomic hydrogen is highly reactive and able to combine with almost any other element.
Protium has no neutrons and is the most abundant of the isotopes of hydrogen. Other isotopes contain one or more neutrons.