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Counting Atoms

Counting Atoms. Counting Atoms. Subscript: the small # after an element symbol. Tells how many atoms there are of that element. Coefficient: the large # before a compound. Tells how many molecules there are. Coefficient. Subscript. 3CaCl 2. Counting Atoms. What is the coefficient?.

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Counting Atoms

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  1. Counting Atoms

  2. Counting Atoms Subscript: the small # after an element symbol • Tells how many atoms there are of that element Coefficient: the large # before a compound • Tells how many molecules there are Coefficient Subscript 3CaCl2

  3. Counting Atoms What is the coefficient? 2 2H2O If there is not a subscript, how many atoms are there? 1

  4. Counting Atoms When a chemical formula has parentheses ( ) …multiply the outside subscript to ALL subscripts inside the parentheses. DO NOT multiply the subscript outside the ( ) to any element not inside the parentheses.. Cu(NO3)2 gives us Cu=1, N=2, and O=6 • Cu is not in ( ) so don’t multiply by 2 • N & O are inside so multiply both their subscripts by 2.

  5. Counting Atoms After you figure out how many atoms in one molecule, if there is a coefficient, multiply by that #. 3CaCl2 • In one molecule, there is Ca=1 and Cl=2, multiply this by the coefficient to get TOTAL in all 3 molecules • 3 x 3 = 9 totals atoms

  6. Counting Atoms Try this one!!! 4Cu(NO3)2 • How many Cu in one molecule? • How many N in one molecule? • How many O in one molecule? • How many total atoms in this molecule? 1 2 6 9 x 4 = 36

  7. More Practice H2SO4 2KNO4 4K2SO4 2Ca3(PO4)2 (NH4)PO4 Ba(OH)2

  8. Counting Atoms WS

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