# Mass of the nucleus

## Homework Statement

The mass of a helium-4 atom is 6.64648310224 g, and each of its two electrons has a mass of 9.10939310228 g. What fraction of this atom’s mass is contributed by its nucleus?

## Homework Equations

fraction of mass = mass of nucleus/mass of atom

## The Attempt at a Solution

I suppose I should calculate the mass of nucleus first. But I only have the mass of the electrons, no mass of neutron, also no density...

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Mass of nucleus = 6.64648310224
Mass of electrons = 9.10939310228 * 2
Mass of atom = 9.10939310228 * 2 + 6.64648310224 = 24.8652693068

Fraction of mass = mass of nucleus/mass of atom = 6.64648310224/24.8652693068 = 0.26729986392797124965341901615185

But the only problem is your data.
The masses of electron is not more than that of proton. And the mass of proton is too much.
I think you forgot to multiply the masses with power of 10s.
Well, this is the solution. Solve it in this way after you correct the data.

Borek
Mentor
9.10939310228 g
That's incorrect on at least two accounts. First, digits after 9.1093 are wrong, second, the end should read not "28" but "e-28" - and this "e-" is what makes the most important difference.

epenguin
Homework Helper
Gold Member
Where is this question from? I find it hard to believe that these masses are known to anything like 12 significant figures.

Borek
Mentor
Where is this question from? I find it hard to believe that these masses are known to anything like 12 significant figures.
9.10938356(11)×10−31 kg, if you copy digits only you will get even 13 sigfigs Mass of nucleus = 6.64648310224
Mass of electrons = 9.10939310228 * 2
Mass of atom = 9.10939310228 * 2 + 6.64648310224 = 24.8652693068

Fraction of mass = mass of nucleus/mass of atom = 6.64648310224/24.8652693068 = 0.26729986392797124965341901615185

But the only problem is your data.
The masses of electron is not more than that of proton. And the mass of proton is too much.
I think you forgot to multiply the masses with power of 10s.
Well, this is the solution. Solve it in this way after you correct the data.
Ohh! I did a mistake
I thought 6.64648310224 is the mass of nucleus.

Correcting it!
Now,
Mass of nucleus = mass of atom - mass of electrons
And after you find it divide it with the mass of atom.

I hope you've verified the data.

• AryaUnderfoot
Borek
Mentor
10-27 kg is not the mass of the proton nor any nucleus.

Ohh! I did a mistake
I thought 6.64648310224 is the mass of nucleus.

Correcting it!
Now,
Mass of nucleus = mass of atom - mass of electrons
And after you find it divide it with the mass of atom.

I hope you've verified the data.
Ah, my bad. I forgot the significant number behind the values..I got it now. Thanks!

And also sorry for late reply ^^