Bunch of Nuclear Physics Question, Please help me.

[Gigacore]

1. What fundamental force will decide the size of an atom?

still I've more to ask. . . waiting for reply

 

[Soff]

There are following fundamental forces:

Gravitation: long distance force
electromagnetic force: Coulomb law
Weak force: is important in beta decay
Strong force: holds nucleons (proton, etc.) together

Since the electrons are kept near the nucleus because of the attractive Coulomb potential, the electromagnetic force decides the size of an atom.

However, in practice, this isn't just the influence of the electromagnetic force which decides the size of the atom. But it plays the leading role.

 

[hasan.phys]

The problem here is what you mean when you say "size of atom". If you mean the effective size of an atom, it goes infinity because of coulomb force, and so coulomb force eleminate the other forces.

 

[blechman]

Of the 4 forces, the only one that matters is E&M - the others are too weak on the atomic scale. You can see this explicitly since the size of an atom is roughly of order the Bohr radius, which goes like 1/e^2 (so the weaker the charge, the larger the atom, as you might expect).