Transcript Chemical Formulas

Chemical Formulas:
The Basics
Subscripts in Chemical Formulas
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Numbers inside formulas.
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Smaller than the font size & lowered below the
line of type.
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Subscripts show the number of atoms of each
element in a representative unit.
Rules for Subscripts in Formulas
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No subscript – it’s understood to be 1.
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Subscripts refer to the element immediately preceding
them.
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Subscripts after parentheses refer to everything
inside ( ).
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 hydrogens
CO2 has ? 1 carbon and 2 oxygens
AgNO3 has ? 1 silver, 1 nitrogen, 3 oxygens
Al(NO3)3 has ? 1 aluminum, 3 nitrogens, and
9 oxygens
No. of atoms in formulas
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Al(NO3)3
Al = 1
N= 1X3=3
O= 3X3=9
Total = 13
Subscript outside ( ) X
subscript inside ( )
=
# of atoms
Hint: Look for uppercase letters!
No. of atoms in formulas
Mg3(PO4)2
 Mg = 3
P= 2X1=2
O= 4X2=8
 Total = 13
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Coefficients
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Numbers in front of formulas
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Refer to everything in the formula
immediately following
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No coefficient? It’s understood to be 1.
Coefficients
2H2O means 2(H2O)
 To count atoms take coefficient X
subscript
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2
X 2 = 4 H’s
 2 X 1 = 2 O’s
Hydrates
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A group of salts that have water molecules
stuffed in the empty spaces
Formulas are distinctive
Ex: CuSO45H2O
 means “is associated with” or PLUS
 Not a true chemical bond, but the structure is
definite so the number of empty spaces is definite
and the number of water molecules is definite
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CuSO45H2O
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Count up the atoms!
1 X Cu
1XS
4XO
10 X H
5XO
5[CuSO45H2O]
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Count up the atoms!
5 X Cu
5XS
20 X O
50 X H
25 X O
Coefficients X
Subscripts