# What does it mean by 1 amu? The mass of a proton?

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What does it mean by 1 amu? the mass of a proton or a neutron or an electron? If the mass of O is 16 amu, then what makes 16 amu in O atom? 16 protons or 16 neutrons or 16 electrons?

Borek
Mentor
There is a clear and unambiguous definition of the amu, have you checked it?

russ_watters
There is a clear and unambiguous definition of the amu, have you checked it?
Where is the definition? I don't see it. Could you provide the link, please?

ZapperZ
Staff Emeritus
Where is the definition? I don't see it. Could you provide the link, please?

I don't quite understand why you did not google this. Is there a reason why?

Zz.

OmCheeto
Gold Member
What does it mean by 1 amu? the mass of a proton or a neutron or an electron? If the mass of O is 16 amu, then what makes 16 amu in O atom? 16 protons or 16 neutrons or 16 electrons?
I would recommend Googling: unified atomic mass unit

And when you find the entry at Wikipedia, pay close attention to one word; "One unified atomic mass unit is approximately the mass of one nucleon"

As, if you do some maths, you will find that Oxygen-16's mass isn't quite what the masses of Oxygen-16's protons, neutrons, and electrons, add up to.

In other words, 1 amu is NOT based on the individual masses of the protons, neutrons, and electrons.

I don't quite understand why you did not google this. Is there a reason why?

Zz.
Thanks a lot for the suggestion.

What does it mean by 1 amu? the mass of a proton or a neutron or an electron? If the mass of O is 16 amu, then what makes 16 amu in O atom? 16 protons or 16 neutrons or 16 electrons?
1 amu is a reference taken by scientists to measure the mass of elements. Actally 1 amu=1/12th mass of one C-12 isotope and 1amu=1.66 *10-24grams

ZapperZ
Staff Emeritus
1 amu is a reference taken by scientists to measure the mass of elements. Actally 1 amu=1/12th mass of one C-12 isotope and 1amu=1.66 *10-24grams

... which is something one can easily find with a simple googling. It was why I asked the OP why he didn't do this in the first place. His response appears to look as if this was not even something that he thought of doing, which I find rather puzzling.

Zz.

Inderjeet Singh1208
@HCverma

I cannot help but notice a pattern on your postings.

You have posted several questions on this forum which have very simple answers. Simple as in the sense, browsing through the book or Google or thinking clearly could have solved them.

Yet in your profile it says that you have completed undergrad in Bsc.

Do these questions suit a person who has completed a degree?

https://www.physicsforums.com/threa...something-having-of-mass.952560/#post-6035200

https://www.physicsforums.com/threa...lorophyll-is-it-possible.952553/#post-6034721

https://www.physicsforums.com/threa...h4-and-1-molecule-of-ch4.952196/#post-6031717