2.3.6

Chemical Formulae

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Chemical Formulae

Instead of writing the element or compound name every time, scientists have symbols for each element, which makes writing about them easier.

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Formulae

  • The formulae for compounds are written by putting the element symbols together in a line with no gaps between them.
  • Because all compounds are made of elements, this is always the case.
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Carbon dioxide

  • Carbon dioxide compound is made of carbon and oxygen atoms. The formula is CO2.
  • The little numbers tell you how many of each atom is in a compound.
  • The number is shown just after the element.
  • If there is no number given on the right of an element, then there is just one atom of it.
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Water

  • Water is made of hydrogen and oxygen atoms. The formula is H2O.
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Magnesium oxide

  • Any metals usually go first, and any oxygens usually go last.
  • The formula of magnesium oxide is:
    • MgO.
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Magnesium chloride

  • MgCl2 is the formula for magnesium chloride, which contains magnesium and chlorine atoms.
    • The ‘l’ is a lower case 'L', and not a capital ‘I’. So the compound has magnesium and chlorine, not magnesium, carbon and iodine.

Jump to other topics

1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

1.3Ecological Relationships & Classification

1.4Digestion & Nutrition

1.5Plants & Photosynthesis

1.6Biological Systems & Processes

2Chemistry

2.1Particles

2.2Chemical Reactions

2.3Atoms, Elements, Compounds

2.4The Periodic Table

2.5Materials & the Earth

2.6Reactivity

2.7Energetics

2.8Properties of Materials

3Physics

3.1Energy

3.2Forces & Motion

3.3Waves

3.4Electricity & Magnetism

3.5Matter

3.6Space Physics

4Thinking Scientifically

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