Hydrogen atom (non relativistic) hydrogen atom was solved for the first time within Feynman's path integral formulation of quantum mechanics. This work greatly extended the range of applicability of Feynman's method. Hydrogen atom A hydrogen atom is an atom of the chemical element hydrogen. The electrically neutral atom contains a single positively charged proton and a single negatively charged electron bound to the nucleus by the Coulomb force. Atomic hydrogen constitutes about 75% of the baryonic mass of the universe. In everyday life on Earth, isolated hydrogen atoms (called "atomic hydrogen") are extremely rare. Instead, hydrogen tends to combine with other atoms
Atom economy yield, because a high-yielding process can still result in substantial byproducts. Examples include the Cannizzaro reaction, in which approximately 50% of the reactant aldehyde becomes the other oxidation state of the target; the Wittig reaction, which uses high-mass phosphorus reagents that ultimately become waste; and the Gabriel synthesis, which produces a stoichiometric quantity of phthalic acid If the desired product has an enantiomer the reaction needs to be sufficiently stereoselective even when atom economy is 100%. A Diels-Alder reaction is an example of a potentially very atom efficient reaction that also can be chemo-, regio-, diastereo- and enantioselective. Catalytic hydrogenation