Atom has slightly more mass than it protons+neutrons?

[netrat]

Just a curious question. I had learnt this fact back in school that overall mass of an Atom is slightly more than combined masses of it protons, neutrons and even electrons which is unexplained by science. is it true?

If yes. How?

[Mr Skeptic]

Uh no. An atom has less mass than the protons and neutrons (and the electrons if you bother to keep track of those). At least for the lighter elements. The difference in mass is equal to the energy released by fusion via the equation E = mc^2. Past iron, the mass per protons and neutrons starts increasing again, and again this increase in mass can be used to calculate the energy released by fission.

[alpha2cen]

It's important question.

I've thought about it till one year.

p n(deuterium) +p n(deuterium)---------------->p2 n2(helium)

.............................................missing mass

The missing mass, where did the missing mass go?

The theory say it turns into the energy.

How to turn into mass----> energy?

No one know the answer.

I'm afraid of saying but its the key of the mass getting step, my guess.

Edited December 7, 2010 by alpha2cen

[swansont]

It's important question.

I've thought about it till one year.

p n(deuterium) +p n(deuterium)---------------->p2 n2(helium)

.............................................missing mass

The missing mass, where did the missing mass go?

The theory say it turns into the energy.

How to turn into mass----> energy?

No one know the answer.

I'm afraid of saying but its the key of the mass getting step, my guess.

 

How to turn mass into other forms of energy? Form a more tightly bound system.

[alpha2cen]

Form a more tightly bound system.

 

It's very difficult question.

'more tightly bound system'

How it is related to mass loss?

Till now we don't know how to get mass in the particle system.

One of objects of present LHC experiment is to solve this question.

Fusion result , more tight nuclear structure is well known, but detail mechanism of mass loss is another problem.

[swansont]

A more tightly bound system has less energy, so it has less mass.

 

Not having confirmed the Higgs as the source of mass is a different question from mass decreasing for a bound system, as is the detail of the mechanism.

[Anura]

Arent atoms mostly empty space?

[swansont]

Arent atoms mostly empty space?

 

Classically thinking, yes. Electrons are small, and they are typically found far from the nucleus (as compared to the size of the nucleus).

[lemur]

Uh no. An atom has less mass than the protons and neutrons (and the electrons if you bother to keep track of those). At least for the lighter elements. The difference in mass is equal to the energy released by fusion via the equation E = mc^2. Past iron, the mass per protons and neutrons starts increasing again, and again this increase in mass can be used to calculate the energy released by fission.

Does this mean that the weak force is only present in elements heavier than iron and only the strong force is present in iron and lighter?

[Sisyphus]

Does this mean that the weak force is only present in elements heavier than iron and only the strong force is present in iron and lighter?

 

No. First of all, the conflict is between the strong force which holds things together and the electrostatic force which wants to force things apart. The strong force is stronger but shorter range, which makes it more dominant in a smaller nucleus but less and less so as the nucleus gets larger.

[D H]

Uh no. An atom has less mass than the protons and neutrons (and the electrons if you bother to keep track of those). At least for the lighter elements.

For all elements. Consider U-238. It has 146 neutrons, 92 protons, and an atom mass of 238.0507826. 146 neutrons and 92 protons have an atomic mass of 239.934513. That 239.934513 amu is 1.88373002 amu or 1,754.68338 MeV more than the atomic mass of U-238. Another way to look at this 1754 MeV is in terms of energy per nucleon. Dividing that energy by 238 yields a binding energy of 7.4 MeV per nucleon. Compare that to the 8.8 MeV per nucleon for iron-56. What happens is that the binding energy per nucleon for stable nuclei increases with increasing mass for lighter elements and then starts decreasing with heavier elements. The binding energy remains positive, however. A nuclide with a negative binding energy cannot exist (for any length of time, that is).