Transcript Chemical Formulas: The Basics

Topic: Chemical Formulas
Subscripts in Chemical Formulas
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numbers inside formulas
lowered below line of type
show # of atoms of each element
No subscript – understood to be 1
S8
8 is the subscript, so there are 8 Sulfur
toms
Chemical Formulas
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H2O has: 2 hydrogens and 1 oxygen
NH3 has: 1 nitrogen and 3 hydrogens
CH4 has ? 1 carbon and 4 hydrogen
CO2 has ? 1 carbon and 2 oxygen
AgNO3 has ? 1 silver, 1 nitrogen, 3 oxygen
# atoms in formulas
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Subscript outside ( ) multiplied by
subscript inside ( ) = # of atoms
Al(NO3)3
Al = 1
N= 1x3=3
O= 3x3=9
Total = 13 atoms
Coefficients
Numbers in front of formulas
 Refers to everything following in
formula
 No coefficient? It’s understood to be 1
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4CO2
4 is the coefficient
Coefficients
2H2O means 2(H2O)
 To count atoms multiply: coefficient x subscript
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2 x 2 = 4 H’s
 2 x 1 = 2 O’s
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Chemical Formulas
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3H2O has: 6 hydrogens and 3 oxygens
2NH3 has: 2 nitrogen and 6 hydrogens
4CH4 has ? 4 carbon and 16 hydrogen
3CO2 has ? 3 carbon and 6 oxygen
2AgNO3 has ? 2 Ag, 2 N, 6 O
HI
CH4
Lets Try one more
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2Al(NO3)3
Hydrates
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group of salts that have water molecules
stuffed in their empty spaces
Ex: CuSO45H2O
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 means “is associated with” or “included”
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DOES NOT refer to multiplication
Not a true chemical bond:
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structure is definite so
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# empty spaces is definite &
# water molecules is definite
CuSO45H2O
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Count up the atoms!
Cu x 1
Sx1
O x 4
H x 10
Ox5
total = 21 atoms
5[CuSO45H2O]
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Count up the atoms!
Cu x 5
Coefficients
x
Subscripts
Sx5
O x 20 (5x4)
H x 50 (5x5x2)
O X 25 (5x5)
total = 105 atoms