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Atomic Structure

Atoms are made up of small subatomic particles.

The three types of subatomic particles are:

  • Protons

  • Electrons

  • Neutrons

Protons are positively charged and neutrons are neutral, meaning they have no charge. Protons and neutrons are found at the centre of an atom called the nucleus.

Electrons are negatively charged. They move in energy levels around the nucleus.

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On the periodic table, the atomic number and mass number of each element is shown.

  • The atomic number is the number of protons in the nucleus. In an atom, the number of positively-charged protons is equal to the number of negatively-charged electrons, giving the atom a zero (or neutral) charge.

  • The mass number of an atom is the number of protons plus neutrons in the nucleus, or the total mass of the nucleus.

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In the example above, the atomic number is 2, meaning that the helium atom has 2 protons and therefore 2 electrons.

The mass number is 4. This tells us that Protons + Neutrons = 4. Since there are 2 protons,the number of neutrons must be 2.