Atom Mass and Volume Distribution

Back to Chemistry Grade 9/10

We've already learned that sub-atomic particles differ based on their charge. Now it's time to learn about another way they differ.

Mass and Volume distribution in an atom

An atom is incredibly small, and so is its mass. Interestingly, its components (protons, neutrons and electrons) do not have the same mass as each other, and the mass of the atom isn't evenly distributed around the atom. Instead, the nucleus provides the mass, and the electrons provide the volume.



But how do the various sub-atomic particles' mass compare to one another? To find this out, we look at their relative mass.

Relative Mass of Protons, Neutrons and Electrons

Protons and neutrons have a very similar mass. The electron's mass is a lot smaller - about 2000 times smaller. In other words, we can say that the relative mass of a proton and neutron is 1, when compared to an electron which is 0.0005. Consequently, electrons do not contribute any significant mass to an atom, which is why we do not include them in the mass number.

Charge Relative Mass
Proton +1 1
Neutron None 1
Electron -1 0.0005


But what are their actual masses? Move on to the next section to find out.