• All matter is made up of atoms.
  • An atom is composed of a core of protons and neutrons, surrounded by orbiting electrons.
  • - For example, the lithium atom, which is designated with the Atomic Number 3 has a core of 3 protons (hence its designation), with 4 neutrons and 3 electrons.

     - The stylized diagram below shows a Lithium atom, with protons in white, neutrons in grey and the small white electrons orbiting about the centre core.

  • Atomic mass is the weight of the neutrons, protons and electrons. Electrons are much smaller and weight much less than protons or neutrons.
  • The particles which make up an atom can have electrical charges. Electrons have a negative charge, and protons have a positive charge. Neutrons are electrically neutral.
  • If the amount of positive and negative charge is balanced, the atom as a whole is neutral (ie. the negative and positive cancel out the effect of each other).
  • If an atom (or molecule) carries a charge it is called an ion. Ions are less stable than neutral atoms and seek a partner to bind to, to form an overall neutral molecule. The bond between two charged atoms is called an ionic bond.
  • A positively charged atom or molecule is called at cation (pronounced cat-ine, not ca-shun) and a negatively charged atom or molecule is called an anion. This allows you to distinguish between ions based on the type of charge.
  • If an atom has no charge (ie. is neutral) it appears stable, but in fact there are other factors that can also influence its stability (ie. chemical stability is a measure of the tendency of an atom or group of atoms to resist change).
  • Electrons can shift from one atom to another (ie. changing the nucleus which they orbit around). If this happens, the atoms involved can become negatively or positively charged. Refer back to the lithium diagram – if one of the electrons was lost, the lithium atom would be positively charged. If an electron was added, the lithium would become negatively charged.

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