Atoms are incredibly small and are mostly empty space. Each atom consists of a nucleus and a cloud of particles called electrons that fly around the nucleus. The nucleus is a cluster of two kinds of particles, protons and neutrons.
All the particles in an atom are very light. Their mass is measured in atomic mass units. Protons and electrons have an electric charge, whereas neutrons do not have an electric charge.The following table compares proton, neutron and electron in terms of their mass and charges. Scroll down the page for more examples and explanations.
The number of protons in an atom can be used to identify the atom.
Every other atom has a different number of protons. For example, since only a sodium atom has 11 protons then any atom with 11 protons would be a sodium atom.
The number of protons in an atom is called its atomic number or proton number. For example, the atomic number of sodium is 11.
Every neutral atom has an equal number of protons and electrons.
This means that the total charge on the protons cancels out the total charge on the electrons and the atom has no overall charge. For example, the sodium atom has 11 protons and 11 electrons and there is no overall charge.
Protons and neutrons, also called nucleons, are located in the nucleus of the atom. The total number of protons and neutrons in an atom is called its nucleon number. For example, the sodium atom has 11 protons and 12 neutrons. The nucleon number for the sodium atom is 11 + 12 = 23.
Isotopes are atoms of the same element, with different numbers of neutrons.
For example, all carbon atoms have 6 protons but some carbon atoms have more neutrons than others.
Carbon-12 has 6 protons, 6 electrons and 6 neutrons.
Carbon-13 has 6 protons, 6 electrons and 7 neutrons.
Carbon-14 has 6 protons, 6 electrons and 8 neutrons.
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