### What are the 10 most abundant elements in the universe by number of atomic nuclei?

• I've seen websites that show the ratios of the 10 most common elements but they compare them by relative mass. I think it's more interesting to know the relative abundances of atomic nuclei because that is what you need to know to understand why the universe has the chemical makeup that it does. What are the 10 most abundant elements in the universe by number of atomic nuclei?

Even it weren't listed exactly as you want it on wikipedia(!), and you only had the ranking by mass; how much work is it to divide by the atomic mass of each element?

Rob Jeffries - I actually realized that I could do that half way through writing my question. But I decided to post it anyways just in case anyone was willing to do it for me (-_-)

• All right, so I took the first list on wikipedia listing the 10 most common elements by mass in parts per million, and did what Rob recommended and here's what I got.

https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements#Abundance_of_elements_in_the_Universe

Hydrogen - 739000amu(H)/1amu(H)=739000 H atoms

Helium - 240000amu(He)/4amu(He)=60000 He atoms

Oxygen - 10400amu(O)/16amu(O)=650 O atoms

Carbon - 4600amu(C)/12amu(C)=383 C atoms

Neon - 1340amu(Ne)/20.1amu(Ne)=66 Ne atoms

Iron - 1090amu(Fe)/55.845amu(Fe)=19.5 Fe atoms

Nitrogen - 960amu(N)/14amu(N)=68.5 N atoms

Silicon - 650amu(Si)/28.1amu(Si)=23 Si atoms

Magnesium, - 580amu(Mg)/24.3amu(Mg)=24 Mg atoms

Sulfur - 440amu(S)/32.1amu(S)=13.7 S atoms

So therefore, the 10 most common elements in the universe by atom, with the relative ratios between them, is;

1.Hydrogen (739000)
2.Helium (60000)
3.Oxygen (650)
4.Carbon (383)
5.Nitrogen (68.5)
6.Neon (66)
7.Magnesium (24)
8.Silicon (23)
9.Iron (19.5)
10.Sulfur (13.7)

If anyone sees a mistake that I made with my reasoning or calculations then please point it out.

The table in wikipedia *shows* the elements ranked by number density for the solar system. This easily allows you to check your methodology. What is the problem with using that table anyway? If your argument is that this is the solar system and not "the universe", well I'm afraid the numbers you have used are not true for the universe either. The abundances in the Milky Way over represent the abundances of metals in the universe. However I'm sure the ranking is ok (and identical to the solar sytem ranking *in the table on wikipedia*).

This source http://www.webelements.com/periodicity/abundance_universe_a/ agrees (almost) with your ordering *for the universe*, but puts Fe and S as equal and Si and Mg as equal. I have no idea what the provenance of these is.

That sounds fine to me, especially with magnesium and silicon as they're so similar in ratio anyways. How did you get your data from the site?

Oh, never mind, I see what you did