Explain Like I'm Five

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How is a chemical 'element' differentiated from it's isotopes? (feddit.uk)

submitted 11 months ago by OmegaMouse@feddit.uk to c/explainlikeimfive@lemmy.world

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It's been a while since I was taught Chemistry, but I was reading something the other day and I couldn't quite get my head around the concept.

So the periodic table shows elements with their atomic numbers (protons) and atomic weight (protons + neutrons). Isotopes have different numbers of neutrons, like carbon-12 and carbon-13 which I believe would have 6 and 7 neurons respectively.

So why is carbon-12 the 'default' option, shown on the periodic table? Is it to do with which version of carbon is the most common? I don't understand how we decide what makes up the pure version of an element/ it's atomic weight as shown on the periodic table

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[–] celestia@sh.itjust.works 2 points 11 months ago

Is is on the basis of isotopic frequency as @Transform2942@lemmy.ml mentioned in their comment.

Since an element’s isotopes have different atomic masses, scientists may also determine the relative atomic mass—sometimes called the atomic weight—for an element. The relative atomic mass is an average of the atomic masses of all the different isotopes in a sample, with each isotope's contribution to the average determined by how big a fraction of the sample it makes up.