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Hydrogen-like atom
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<p> A hydrogen-like atom (or hydrogenic atom) is any <a href="/facts/Atom/FoQ4kGN5">atom</a> or <a href="/facts/Ion/3bePpDna">ion</a> with a single <a href="/facts/Valence_electron/mXPA15VP">valence electron</a>. These atoms are <a href="/facts/Isoelectronic/SbzuaI05">isoelectronic</a> with <a href="/facts/Hydrogen_atom/ncVpPbuE">hydrogen</a>. Examples of hydrogen-like atoms include, but are not limited to, <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> itself, all <a href="/facts/Alkali_metals/IkWbCLk2">alkali metals</a> such as <a href="/facts/Rubidium/KDHSe2HM">Rb</a> and <a href="/facts/Caesium/dXKN1S5k">Cs</a>, singly ionized <a href="/facts/Alkaline_earth_metals/Ts4U5zIe">alkaline earth metals</a> such as <a href="/facts/Calcium/hf252CC0">Ca+</a> and <a href="/facts/Strontium/ABaA5qQK">Sr+</a> and other ions such as <a href="/facts/Helium/yRul93TG">He+</a>, <a href="/facts/Lithium/7vXX6BWA">Li2+</a>, and <a href="/facts/Beryllium/dv295voP">Be3+</a> and <a href="/facts/Isotopes/KD9B1y6o">isotopes</a> of any of the above. A hydrogen-like atom includes a positively charged core consisting of the <a href="/facts/Atomic_nucleus/orpIm5Xl">atomic nucleus</a> and any <a href="/facts/Core_electron/LQuGLKcG">core electrons</a> as well as a single valence electron. Because helium is common in the universe, the spectroscopy of singly ionized helium is important in <a href="/facts/Extreme_ultraviolet/tRW9pqeI">EUV</a> astronomy, for example, of DO <a href="/facts/White_dwarf/gIYlTtrC">white dwarf</a> stars. </p><p>The non-relativistic <a href="/facts/Schr%25C3%25B6dinger_equation/3csgSIWF">Schrödinger equation</a> and relativistic <a href="/facts/Dirac_equation/DzFaXS4p">Dirac equation</a> for the hydrogen atom can be solved analytically, owing to the simplicity of the two-particle physical system. The one-electron <a href="/facts/Wave_function/KgM5ykjY">wave function</a> solutions are referred to as <i>hydrogen-like atomic orbitals</i>. Hydrogen-like atoms are of importance because their corresponding orbitals bear similarity to the hydrogen atomic orbitals. </p><p>Other systems may also be referred to as "hydrogen-like atoms", such as <a href="/facts/Muonium/dnnS0EbC">muonium</a> (an electron orbiting an <a href="/facts/Muon/BP2fLVIR">antimuon</a>), <a href="/facts/Positronium/F35JBo9C">positronium</a> (an electron and a <a href="/facts/Positron/HgV4zBzA">positron</a>), certain <a href="/facts/Exotic_atom/FrPmnXvk">exotic atoms</a> (formed with other particles), or <a href="/facts/Rydberg_atom/yUrerWYz">Rydberg atoms</a> (in which one electron is in such a high energy state that it sees the rest of the atom effectively as a <a href="/facts/Point_charge/4MPToN8W">point charge</a>). </p>