Talk:Atomic mass

Stylized lithium-7 atom?

The picture of the Stylized lithium-7 atom has (3) electrons each at equal distance orbit from the nucleus, which seems misleading. Is there a case in real life where you could force all (3) electrons in lithium-7 to have equal energy and be stable in a single electron shell? Even in the bohr model, you'd expect (2) shells, not a single shell. A picture of a Quantum model of lithium-7 I think would be better. Or at least a picture showing (2) electron shells... Goslackware (talk) 17:27, 4 October 2023 (UTC)

Is there a case in real life where you could force all (3) electrons in lithium-7 to have equal energy and be stable in a single electron shell?

The Pauli exclusion principle says definitely no. However the electronic structure of the atom is not relevant to this particular article, and a more accurate diagram might get in the way of the intended meaning. FChlo (talk) 01:27, 16 January 2024 (UTC)

Explain jargon: numbers in parenthesis

I noticed numbers in parenthesis, for example "1.007825031898(14)". What does that (14) part mean? It's not a common way to write numbers, so it should be explained. Mateussf (talk) 12:39, 19 June 2024 (UTC)

It's a common way to express uncertainty, named "concise notation", ex. https://www.physics.nist.gov/cgi-bin/cuu/Value?u|search_for=atomic+mass

Read more about uncertainty here: https://www.physics.nist.gov/cgi-bin/cuu/Info/Constants/definitions.html

~~ 85.24.253.39 (talk) 18:58, 20 May 2025 (UTC)

Relative Isotopic Mass, Carbon-12

4th Paragraph. "... the atomic mass of a carbon-12 atom is 1.99264688270(62)×10−26 kg." I was expecting the value be 0.001 the reciprocal of Avagadro's number: ~1.66054 E-27 kg. Multiple other internet sources quote the atomic mass of C12 as 1.66054 E-27 kg. The value state here appears to be exactly 12x larger. In addition to correcting the error, mentioning the relationship to Avagadro's number would seem to be a good addition in this section. 2600:1700:BFA1:8690:4C9F:D8EB:EC4E:151 (talk) 05:46, 29 July 2025 (UTC)

Avogadro's number is the number of atoms in one mole of a substance and was historically defined so that 1 mole = ⁠$N_{A}$⁠ atoms of carbon-12 has a mass of exactly 12 grams. This empirical definition was rendered obsolete by the 2019 redefinition of SI units, but is still correct to several decimal places, so the mass of one carbon-12 atom – 12 Daltons – should be about ⁠${\frac {12}{1000N_{A}}}~{\text{kg}}\approx 1.99\cdot 10^{-26}~{\text{kg}}$⁠, which is the stated value in the article. The number you state, 1.66×10⁻²⁷ kg, is instead the mass of one Dalton, or approximately (to within 1%) the mass of one hydrogen-1 atom. ^Complex/_Rational 02:12, 31 July 2025 (UTC)