Chemistry » Essential Ideas in Chemistry » Structure of the Atom

The Nucleus

The Nucleus

Unlike the electron, the nucleus can be broken up into smaller building blocks called protons and neutrons. Together, the protons and neutrons are called nucleons.

Did You Know?

Scientists believe that the electron can be treated as a point particle or elementary particle meaning that it cannot be broken down into anything smaller.

The Proton

The electron carries one unit of negative electric charge (i.e. \(-\text{1.6} \times \text{10}^{-\text{19}}\) \(\text{C}\), C is Coulombs).

Each proton carries one unit of positive electric charge (i.e. \(\text{+1.6} \times \text{10}^{-\text{19}}\) \(\text{C}\)). Since we know that atoms are electrically neutral, i.e. do not carry any extra charge, then the number of protons in an atom has to be the same as the number of electrons to balance out the positive and negative charge to zero. The total positive charge of a nucleus is equal to the number of protons in the nucleus. The proton is much heavier than the electron (\(\text{10 000}\) times heavier!) and has a mass of \(\text{1.6726} \times \text{10}^{-\text{27}}\) \(\text{kg}\). When we talk about the atomic mass of an atom, we are mostly referring to the combined mass of the protons and neutrons, i.e. the nucleons.

The Neutron

The neutron is electrically neutral i.e. it carries no charge at all. Like the proton, it is much heavier than the electron and its mass is \(\text{1.6749} \times \text{10}^{-\text{27}}\) \(\text{kg}\) (slightly heavier than the proton).

Table: Summary of the Particles Inside the Atom





Mass (\(\text{kg}\))

\(\text{1.6726} \times \text{10}^{-\text{27}}\)

\(\text{1.6749} \times \text{10}^{-\text{27}}\)

\(\text{9.11} \times \text{10}^{-\text{31}}\)

Units of charge




Charge (\(\text{C}\))

\(\text{1.6} \times \text{10}^{-\text{19}}\)


\(-\text{1.6} \times \text{10}^{-\text{19}}\)

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