Fundamental chemical concepts
The chemical formula of a compound tells you how many atoms of each element the molecule contains.
|name||formula||sodium atoms||hydrogen atoms||carbon atoms||sulfur atoms||oxygen atoms|
The small 2 after an element tells you there are two atoms of that particular element in each molecule. For example, the water molecule H2O has two hydrogen atoms. Notice that you do not write a number 1 if there is only one atom of an element in a molecule.
Some formulas have brackets in them. For example, sodium hydroxide is NaOH, but magnesium hydroxide is Mg(OH)2. The 2 outside the brackets tells you that you have two of each atom inside the bracket. So in Mg(OH)2 you have one magnesium atom, two oxygen atoms and two hydrogen atoms. The table shows some more examples of these formulas.
|name||formula||iron atoms||oxygen atoms||hydrogen atoms|
|iron(III) hydroxide||Fe(OH)3||1||1 × 3 = 3|
|iron(II) nitrate||Fe(NO3)2||1||1 × 2 = 2||3 × 2 = 6|
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