Editing Mole (unit) (section)

=== 2019 revision of the SI ===

Before the [[2019 revision of the SI]], the mole was defined as the amount of substance of a system that contains as many elementary entities as there are atoms in 12 [[gram]]s of [[carbon-12]] (the most common [[isotopes of carbon|isotope of carbon]]).<ref name=SI8>{{SIbrochure8th}}</ref>
The term ''gram-molecule'' was formerly used to mean one mole of molecules, and ''gram-atom'' for one mole of atoms.<ref name="SI114-15">{{SIbrochure8th|pages=114–15}}</ref> For example, 1 mole of [[MgBr2|MgBr<sub>2</sub>]] is 1&nbsp;gram-molecule of MgBr<sub>2</sub> but 3&nbsp;gram-atoms of MgBr<sub>2</sub>.<ref>
{{cite journal
| doi=10.1088/0953-8984/15/6/315
| last1=Wang | first1=Yuxing
| last2=Bouquet | first2= Frédéric
| last3=Sheikin | first3=Ilya
| last4=Toulemonde | first4=Pierre
| last5=Revaz | first5=Bernard
| last6=Eisterer | first6=Michael
| last7=Weber | first7=Harald W.
| last8=Hinderer | first8=Joerg
| last9=Junod | first9=Alain
| display-authors=etal
| title=Specific heat of MgB<sub>2</sub> after irradiation
| journal=Journal of Physics: Condensed Matter | year=2003
| volume=15
| issue=6 | pages=883–893|arxiv = cond-mat/0208169 |bibcode = 2003JPCM...15..883W| s2cid=16981008 }}</ref><ref>{{cite journal
| doi=10.1103/PhysRevB.72.024547
| last1=Lortz | first1=R.
| last2=Wang | first2=Y.
| last3=Abe | first3=S.
| last4=Meingast | first4=C.
| last5=Paderno | first5=Yu.
| last6=Filippov | first6=V.
| last7=Junod | first7=A.
| display-authors=etal
| title=Specific heat, magnetic susceptibility, resistivity and thermal expansion of the superconductor ZrB<sub>12</sub>
| journal=Phys. Rev. B | year=2005
| volume=72
| issue=2 | pages=024547
| arxiv = cond-mat/0502193
| bibcode = 2005PhRvB..72b4547L
| s2cid=38571250
}}</ref>

In 2011, the 24th meeting of the [[General Conference on Weights and Measures]] (CGPM) agreed to a plan for a possible revision of the [[SI base unit]] definitions at an undetermined date.

On 16 November 2018, after a meeting of scientists from more than 60 countries at the CGPM in Versailles, France, all SI base units were defined in terms of physical constants. This meant that each SI unit, including the mole, would not be defined in terms of any physical objects but rather they would be defined by [[physical constant]]s that are, in their nature, exact.<ref name="IUPACrev" />

Such changes officially came into effect on 20 May 2019. Following such changes, "one mole" of a substance was redefined as containing "exactly {{val|6.02214076|e=23}} elementary entities" of that substance.<ref>[https://www.bipm.org/utils/en/pdf/CIPM/CIPM2017-EN.pdf?page=23 CIPM Report of 106th Meeting] {{webarchive|url=https://web.archive.org/web/20180127202612/https://www.bipm.org/utils/en/pdf/CIPM/CIPM2017-EN.pdf?page=23 |date=2018-01-27 }} Retrieved 7 April 2018</ref><ref>{{cite journal |title=Redefining the Mole |url=https://www.nist.gov/si-redefinition/redefining-mole |journal=NIST |access-date=24 October 2018|date=2018-10-23 }}</ref>