Particles

KEY POINTS:

• Over 2,400 years ago Democritus and a few other highly intelligent philosophers proposed that matter was made from atoms (from the word atomos – the smallest unit in science).
• Atoms are much too small to be seen. Atomic theory is precisely that, i.e. we cannot see the atoms but we have evidence that suggest their existence. In future years this may be rejected.
• A chemical element is a pure substance made of one type of atom only. All of the known elements are found in the periodic table.
• When atoms join together via chemical bonds, they form molecules.
• Diatomic molecules are made of two identical atoms, e.g. oxygen, represented as O₂.
• If the atoms that are bonded together are different, you have a chemical compound, e.g. sodium chloride, represented as NaCl.
• Mixtures of elements and compounds all come together to form the universe as we know it – from the hydrogen gas fusing together to from helium in our sun at the centre of the solar system, to the strands of DNA that provide the genetic blueprint for organic life.