Editing Proton (section)

== Proton in chemistry ==

=== Atomic number ===
In [[chemistry]], the number of protons in the [[atomic nucleus|nucleus]] of an atom is known as the [[atomic number]], which determines the [[chemical element]] to which the atom belongs. For example, the atomic number of [[chlorine]] is 17; this means that each chlorine atom has 17 protons and that all atoms with 17 protons are chlorine atoms. The chemical properties of each atom are determined by the number of (negatively charged) [[electron]]s, which for neutral atoms is equal to the number of (positive) protons so that the total charge is zero. For example, a neutral chlorine atom has 17 protons and 17 electrons, whereas a Cl<sup>−</sup> [[anion]] has 17 protons and 18 electrons for a total charge of −1.

All atoms of a given element are not necessarily identical, however. The [[number of neutrons]] may vary to form different [[isotope]]s, and energy levels may differ, resulting in different [[nuclear isomer]]s. For example, there are two stable [[isotopes of chlorine]]: {{nuclide|Chlorine|35}} with 35 − 17 = 18 neutrons and {{nuclide|Chlorine|37}} with 37 − 17 = 20 neutrons.

=== Hydrogen ion ===
{{See also|Hydron (chemistry)}}
[[File:Hydrogen.svg|thumb|220px|Protium, the most common isotope of hydrogen, consists of one proton and one electron (it has no neutrons). The term ''hydrogen ion'' ({{chem|H|+}}) implies that that H-atom has lost its one electron, causing only a proton to remain. Thus, in chemistry, the terms ''proton'' and ''hydrogen ion'' (for the protium isotope) are used synonymously.]]

{{quote box|width=20%|align=left|quote=The proton is a unique chemical species, being a bare nucleus. As a consequence it has no independent existence in the condensed state and is invariably found bound by a pair of electrons to another atom.|salign=right|source=Ross Stewart, ''The Proton: Application to Organic Chemistry'' (1985, p. 1)}}
In chemistry, the term ''proton'' refers to the hydrogen ion, {{chem|H|+}}. Since the atomic number of hydrogen is 1, a hydrogen ion has no electrons and corresponds to a bare nucleus, consisting of a proton (and 0 neutrons for the most abundant isotope ''protium'' {{nuclide|Hydrogen|1|link=yes}}). The proton is a "bare charge" with only about 1/64,000 of the radius of a hydrogen atom, and so is extremely reactive chemically. The free proton, thus, has an extremely short lifetime in chemical systems such as liquids and it reacts immediately with the [[electron cloud]] of any available molecule. In aqueous solution, it forms the [[hydronium ion]], H<sub>3</sub>O<sup>+</sup>, which in turn is further [[solvation|solvated]] by water molecules in [[Hydrogen ion#Cation (positively charged)|clusters]] such as [H<sub>5</sub>O<sub>2</sub>]<sup>+</sup> and [H<sub>9</sub>O<sub>4</sub>]<sup>+</sup>.<ref name="Headrick2005" />

The transfer of {{chem|H|+}} in an [[Brønsted–Lowry acid–base theory|acid–base reaction]] is usually referred to as "proton transfer". The [[acid]] is referred to as a proton donor and the [[base (chemistry)|base]] as a proton acceptor. Likewise, [[biochemistry|biochemical]] terms such as ''[[proton pump]]'' and ''[[proton channel]]'' refer to the movement of hydrated {{chem|H|+}} ions.

The ion produced by removing the electron from a [[deuterium]] atom is known as a ''deuteron'', not a proton. Likewise, removing an electron from a [[tritium]] atom produces a ''triton''.

=== Proton nuclear magnetic resonance (NMR) ===
Also in chemistry, the term ''[[proton NMR]]'' refers to the observation of hydrogen-1 nuclei in (mostly [[organic chemistry|organic]]) molecules by [[nuclear magnetic resonance]]. This method uses the [[Quantization (physics)|quantized]] [[spin magnetic moment]] of the proton, which is due to its angular momentum (or [[Spin (physics)|spin]]), which in turn has a magnitude of one-half the reduced [[Planck constant]]. (<math>\hbar/2</math>). The name refers to examination of protons as they occur in [[Hydrogen-1|protium]] (hydrogen-1 atoms) in compounds, and does not imply that free protons exist in the compound being studied.