1.3 - Charges and masses of subatomic particles
Compare the charges and masses of protons, neutrons and electrons. You will use the relative values correctly without confusing electric charge with mass.
Reading relative values
Relative values compare a quantity with a reference instead of giving its value in grams or coulombs. Relative charge uses the size of the proton’s charge as one unit. The plus and minus signs indicate opposite types of charge.
For the rounded mass comparison used here, a proton and a neutron each have relative mass about 1. An electron has about 1/1840 of that mass. None of these numbers is a mass in grams.
| Particle | Relative charge | Relative mass (approximate) |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | −1 | 1/1840 |
The electron’s mass is often called negligible when estimating an atom’s total mass: its contribution is small enough to ignore in that estimate. This does not mean its mass is exactly zero.
Charge and mass are different properties
A proton and electron have charges of equal size and opposite sign, even though their masses differ greatly. A neutron has no charge but has almost the same mass as a proton. Therefore neither the sign nor the size of charge tells you the mass.