An atom, which is the smallest unit of all matter, consists of a nucleus and an outer region.
The nucleus at the centre of an atom contains nucleons (protons and neutrons), and is surrounded by electrons orbiting in the outer region.
A neutral or stable atom has an equal number of protons and electrons.
The nucleus at the centre of an atom contains nucleons (protons and neutrons), and is surrounded by electrons orbiting in the outer region.
A neutral or stable atom has an equal number of protons and electrons.
The number of protons, also called the atomic number, is written as a subscript to the left of the element symbol.
In contrast, the total number of protons and neutrons, also called the nucleon number or mass number, is written as a superscript to the left of the element symbol.
