1.15 Subatomic particles

1.15 Sub atomic particles

Students should:

1.15 know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles.

Here we look at the particles inside the atom. Sub atomic particles are the particles found inside atoms. These include protons, neutrons and electrons:

protons are particles with a positive charge (+1) and a mass of 1 atomic mass unit (amu) . They are part of the nucleus of an atom.
The number of protons is given by the atomic number of an element.
neutrons are particles with no charge and a mass of 1(amu) they are also part of the nucleus of an atom.
electrons are particles with a negative charge (-1 ) and a mass of 1/2000 of an amu, they orbit the nucleus in shells.

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1.15 Into orbit

This animation shows an atom of carbon, we know it is carbon because it has six protons shown in the nucleus.

The number of protons in the nucleus is given by the atomic number - ( also known as the proton number). You can find this on the periodic table.

The mass number of an atom is the total number of protons and neutrons. In this case, the nucleus has six neutrons and the atom therefore, has a mass number of 6 + 6 = 12.

Atoms with the same number of protons but a different number of neutrons can exist. These are known as isotopes of the element.

Carbon has three isotopes, Carbon 12, Carbon 13 and carbon 14. These are described in more detail in the next section: