Transcript Chemical Formulas: The Basics

Chemical Formulas:
The Basics
Subscripts in Chemical Formulas
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numbers inside formulas
found below line of type
show # of atoms of each element in formula
Rules for Subscripts in Formulas
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no subscript: understood to be 1
subscripts refer to element immediately
preceding (before) number
subscripts after parentheses refer to
everything inside ( )
Chemical Formulas
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H2O: 2 hydrogen and 1 oxygen
NH3: 1 nitrogen and 3 hydrogen
CH4 has ? 1 carbon and 4 hydrogen
CO2 has ? 1 carbon and 2 oxygen
AgNO3 has ? 1 silver, 1 nitrogen, 3 oxygen
reminder: subscript outside ( ) multiplied by
subscript inside ( ) = # of atoms
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Al(NO3)3
Al = 1
N= 1x3=3
O= 3x3=9
total = 13 atoms
Coefficients
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numbers in front of formulas
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refers to everything following in formula
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no coefficient? understood to be 1
Coefficients
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5H2O means:
H2O + H2O + H2O + H2O + H2O
to count atoms:
multiply: coefficient x subscript
5 x 2 = 10 H’s
 5 x 1 = 5 O’s
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Hydrates
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group solid salts that have water molecules
incorporated into their empty spaces
formulas are distinctive
ex: CuSO45H2O
 means H2O “is associated with” or “included”
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DOES NOT refer to multiplication
true chemical bond:
structure is definite
number empty spaces is definite
number water molecules is definite
CuSO45H2O
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count up the atoms!
1 Cu
1S
4 O + (5x1) O = 9 O
(5x2) H =10 H
total = 21 atoms
5CuSO45H2O
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count up the atoms!
5 = Cu
5=S
(5x4) O + (5x5x1) O = 45 O
(5x5x2) H = 50 H
total = 105 atoms