Proton

A proton is a subatomic particle in the nucleus with a relative mass of 1 and a relative charge of +1. Malay: proton · Chinese: 质子.

The proton is one of the three subatomic particles, together with the neutron and the electron. Its positive charge is what makes the nucleus positive, and its relative mass of 1 means it contributes, along with the neutron, almost all of the atom’s mass. Most importantly, the number of protons in an atom, its proton number, is fixed for each element and is what tells you which element the atom is.

Example. Every hydrogen atom has exactly 1 proton, and every carbon atom has exactly 6 protons. If a neutral atom is found to have 11 protons, it can only be sodium, because no other element has 11 protons. In that neutral atom the number of electrons also equals 11, since protons and electrons balance.

Confusion to avoid. Do not confuse the proton with the neutron or the electron. The proton has charge +1 and mass 1; the neutron has the same mass but no charge; the electron has charge −1 and a mass so small it is ignored. Students also mix up a proton (the particle) with the proton number (the count of protons), keep the particle and the number separate in your wording.

In the exam you are often asked to state the relative mass and relative charge of each subatomic particle in a table, and the proton’s values, mass 1, charge +1, are the reference point for the others. You may also be given the number of protons and asked to name the element, or given the element and asked for its proton number from the Periodic Table.

Because the proton number defines the element and equals the number of electrons in a neutral atom, the proton sits at the centre of everything in the Matter and the Atomic Structure chapter, from the Periodic Table to electron arrangement. Once students can read a proton number off the Periodic Table with confidence, the rest of atomic structure follows quickly.