COUNT ATOM

1
COUNT ATOM

• How to count atoms

2

• 2H2O

COEFFICIENT
SUBSCRIPT
3
2H2O

• The coefficient gets applied to the ENTIRE
  formula
• -this means that there are 2 molecules of water
  present!
• -you MULTIPLY this number by every subscript in
  the formula

4
2H2O
2MOLECULES!!!!
5
2H2O

• The subscript only gets applied to the element it
  follows
• -If there is no subscript present, it is assumed
  that there is only 1 atom of that element in the
  molecule.

6
2H2O

• How many hydrogen atoms are present?
• 4
• How many oxygen atoms are present?
• 2

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The easiest way to count atoms

• 1. Write down all of the symbols for all of the
  elements present in the formula
• 2. If there is a coefficient, write this number
  next to each of the symbols
• 3. Multiply the coefficient by the subscripts of
  each of the elements present in the formula

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Lets try an example

• 4CaCO3

9
4CaCO3
10
1. Write down symbols
4CaCO3
Ca C O
11
Write down the coefficient next to each symbol
4CaCO3
Ca C O
4 4 4
12
Multiply by the subscript
4CaCO3
Ca C O
4 4 4
X X X
1 1 3
13
Multiply
4CaCO3
Ca C O
4 4 4
X X X
1 1 3

4 4 12
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Add totals together to get the total amount of
atoms

• 4CaCO3

Ca C O
4 4 4
X X X
1 1 3

4 4 12 20 atoms
15
3CO2
16
3CO2
17
2C6H12O6
GLUCOSE
18
2C6H12O6
19
6K2SO4
20
6K2SO4
21
CaMg(CO3)2
22
CaMg(CO3)2
23
3Pb(NO3)2
24
3Pb(NO3)2