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Counting Atoms
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How to Count Atoms The symbol of an element represents one atom of that element. e.g. Na = 1 atom
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A subscript is a number written at the lower right corner behind the symbol of an element. If there is more than one atom of the element, then a subscript is used to indicate the number of atoms. e.g. H2 = 2 atoms
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A subscript outside a bracket multiplies all the elements inside the brackets.
e.g. Mg3(PO4)2 : Mg = 3 atoms P = 2 atoms O = 8 atoms Total Atoms: 13
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(a) A coefficient is a number written in front of a chemical symbol and indicates the number of atoms of that element. e.g. 3 C = 3 atoms OR
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(b) A coefficient is a number written in front of a chemical formula and indicates the number of that compound. NOTE: A coefficient multiplies the number of atoms of each element in the formula.
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Examples 2 H2O 4 Hydrogen atoms 2 Oxygen atoms Total Atoms: 6
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3 CuSO4 3 copper 3 Sulphur 12 Oxygen atoms Total Atoms: 18
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4 Pb(NO3)2 4 lead 8 Nitrogen 24 Oxygen atoms Total: 36
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Homework Complete two worksheets on counting atoms Remember:
Element Project is due Nov 2 3D box needs to be handed in after you give your 3 min presentation
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