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Atoms, protons, neutrons and electrons

The atom is the most basic particle of a chemical element that exhibits the properties of the element. Atoms are made of three subatomic particles: protons, neutrons and electrons.

Protons are positively charged, neutrons are uncharged (neutral) and electrons are negatively charged.

Protons and neutrons are also called nucleons, since they make up the atomic nucleus.

A proton and a neutron each have approximately the same mass. An electron has a much smaller mass ($$\displaystyle{\frac{1}{1837}}$$ of a proton).

The image shows the model of a helium atom ($$\ce{He}$$). At the centre is the nucleus, with two neutrons and two protons (represented by green and orange circles).

There are two electrons (shown as blue circles) in the electron shell.