COMPOUNDS
A compound is a pure substance made from two or more different elements.
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Elements in a compound are joined in fixed amounts.
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A compound has different properties from the elements it is made from.
Examples of Compounds
| Compound | Elements Present |
|---|---|
| Water | Hydrogen, Oxygen |
| Carbon dioxide | Carbon, Oxygen |
| Sodium chloride | Sodium, Chlorine |
| Copper carbonate | Copper, Carbon, Oxygen |
| Glucose | Carbon, Hydrogen, Oxygen |
| Ammonia | Hydrogen, Nitrogen |
| Potassium nitrate | Potassium, Nitrogen, Oxygen |
| Methane | Carbon, Hydrogen |
Element vs Compound
| Element | Compound |
|---|---|
| One kind of atom | Two or more different elements |
| Cannot be split chemically | Can be split into elements chemically |
| Represented by symbols | Represented by formulae |
Chemical Formula
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A chemical formula shows the types and numbers of atoms in a compound.
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Numbers are shown as subscripts (small numbers below the symbol).
Example:
Glucose: C₆H₁₂O₆
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6 Carbon atoms
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12 Hydrogen atoms
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6 Oxygen atoms
Common Chemical Formulae
| Substance | Formula |
|---|---|
| Carbon dioxide | CO₂ |
| Water | H₂O |
| Ethanol | C₂H₅OH |
| Sodium chloride | NaCl |
| Copper(II) sulphate | CuSO₄ |
Determining Atoms in a Formula
Example 1:
Sucrose → C₁₂H₂₂O₁₁
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Carbon: 12
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Hydrogen: 22
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Oxygen: 11
Example 2:
Sodium sulphate → Na₂SO₄
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Sodium: 2
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Sulphur: 1
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Oxygen: 4
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Total atoms = 7