which does the most

Question

. Which contributes more to an atom’s mass: electrons or
protons? Which contributes more to an atom’s size?

Answer 1

Hi Richard;

 

The proton contributes more to an atom's mass as its weight is 1 atomic mass unit (amu), whereas the amu of an electron is a fraction of that.  However, it is the electron(s) which are orbiting around the protons as the latter are positioned in the nucleus of the atom with the neutrons.  Such neutrons each also have an amu of 1.  Henceforth, the electron contributes more substantially to the atom's size.

Answer 2

Despite how awkward it really is as a model, look at the Bohr model of an atom. In the two-dimensional representation, most of the outer parts of the model are where the electrons exist, while the inner-most area is the cluster of protons and neutrons. Look into the Rutherford gold foil experiment for more support of this answer.

 

and the other part:

proton mass = 1.7 x 10^-27 kg (1 atomic mass unit)

electron mass = 9.1 x 10^-31 kg (0.00055 atomic mass units)