Hydrogenic: definition in chemistry
Hydrogenic: Describes an atom or ion that, like hydrogen, has only one electron, such as He⁺ or Li²⁺. Such a species is also called a hydrogen-like atom.
With only one electron there is no repulsion between electrons, so the Schrödinger equation can be solved exactly, giving energy levels of −13.6 eV × Z²/n², where Z is the nuclear charge and n the shell number. In a hydrogenic atom, all orbitals in the same shell, such as 2s and 2p, have the same energy. Hydrogenic orbitals are the starting point for describing the more complicated orbitals of atoms with many electrons.
Examples
- Hydrogen (H) — the simplest hydrogenic atom
- He⁺ — needs 54.4 eV to remove its electron, four times hydrogen's 13.6 eV
- Li²⁺ — a lithium nucleus with a single electron
- U⁹¹⁺ — uranium stripped of all but one electron in particle accelerators
On the periodic table
Any element can in principle form a hydrogenic ion by losing all but one electron, so an element with atomic number Z gives an ion with a charge of (Z − 1)+.