Chemical Formulas and

1
Chapter 7

• Chemical Formulas and
• Chemical Compounds

2
Section 1 Chemical Names Formulas

• There are literally thousands of chemicals
• Isnt always best to use common names for
  chemicals (calcium carbonate is limestone, sodium
  chloride is salt, and hydrogen oxide is water)
• Common names dont give information about
  chemical composition.

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Section 1 Chemical Names Formulas

• Significance of chemical formulas
• Gives relative number of atoms of each kind of
  element.
• Subscripts small numbers to the right that tell
  the number of atoms
• If no subscript then it is understood to be 1
• H2SO4
• 2 hydrogens, 1 sulfur, 4 oxygen

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Section 1 Chemical Names Formulas

• When parentheses are used you must multiply
  inside and out.
• Al2(SO4)3
• (2 Aluminums, 3 Sulfurs, 12 Oxygens)

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Section 1 Names of Binary Compounds

• Binary compounds are those formed from only 2
  elements.
• To write their formulas the positive ion is
  written first and then the negative.
• To name them use the complete name of the
  positive ion and add the negative ion name but
  change the ending to -ide. (Sulfur becomes
  sulfide, oxygen becomes oxide, phosphorous
  becomes phosphide)

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Section 1 Formulas of Binary Compounds

• To write the formula of a compound you must
  consider the charges and multiply by adding
  subscripts so that the overall charge on the
  compound is zero.
• Ex zinc is (2) and sulfur is (2-) so
• ZnS
• Name Zinc Sulfide

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Section 1 Formulas of Binary Compounds

• Ex zinc is (2) and iodine is (1-) so
• Zn 2 I 1-
• ZnI2
• Name Zinc Iodide

2 2- ( 0 )
Subscripts1 2
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Section 1 Formulas of Binary Compounds

• How do you know the charge?
• Use the valence electrons
• Group 1 1, Group 2 2, 3, 4
• Group 15 3-, Grp. 16 2-, Grp. 17 1-
• May use charge chart (page 205) for transition
  metals.

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Assignment

• Worksheet Writing formulas and names for binary
  compounds.

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Section 1 Stock System of Nomenclature

• Some transition metals have more than one
  possible charge
• Ex. Copper Cu and Cu2
• Iron Fe2 and Fe3
• Lead Pb3 and Pb4
• Tin Sn2 and Sn4

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Section 1 Stock System of Nomenclature

• The charges of these elements must be represented
  in the name of the compounds.
• Charges are provided by using Roman numerals in
  the names
• Ex Iron (II) oxide and Iron (III) oxide
• Formulas FeO Fe2O3

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Section 1 Stock System of Nomenclature

• How do you know how to write the formula???
• Iron (II) combines with oxygen
• Fe2 O2- (charges equal zero so FeO)
• Iron (III) combines with oxygen
• Fe3 O2- (add subscripts and multiply
  to equal zero

2 3
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Section 1 Stock System of Nomenclature

• How do you know how to write the name if you only
  see the formula???
• CuBr2
• The name is Copper Bromide but is it Copper (I)
  Bromide or Copper (II) Bromide???

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Section 1 Stock System of Nomenclature
Then 1 -2 ? 0
If charges are 1 -1

• Cu Br2

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Section 1 Stock System of Nomenclature
Then 2 -2 0
If charges are 2 -1

• Cu Br2

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Assignment

• Worksheet
• Naming and Writing Formulas for Compounds Using
  the Stock System

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Section 1 Naming Binary Molecular Compounds

• Molecular compounds are those in which the
  elements are close together on the periodic
  table.
• Ex
• Nitrogen and Oxygen
• Carbon and Oxygen
• Sulfur and Oxygen
• Phosphorus and Chlorine

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Section 1 Naming Binary Molecular Compounds

• Ex Compounds of Nitrogen and Oxygen
• N2O
• NO
• NO2
• N2O3
• N2O5
• Newer method of naming is to use the stock system
  with Roman Numerals.
• Old traditional method uses prefixes.

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Section 1 Naming Binary Molecular Compounds

• Prefixes indicate the number of atoms in the
  compound
• 1 atom Mono
• 2 atoms Di
• 3 atoms Tri
• 4 atoms Tetra
• 5 atoms Penta
• 6 atoms Hexa
• 7 atoms Hepta
• 8 atoms Octa
• 9 atoms Nona
• 10 atomsDeca

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Section 1 Naming Binary Molecular Compounds

• The less electronegative element is written first
  and is given a prefix only if it has more than
  one atom in the formula.
• Next element has a prefix indicating the number
  of atoms and ends typically with ide.
• Examples
• N2O
• NO
• NO2
• N2O3
• N2O5

Dinitrogen Monoxide
Nitrogen Monoxide
Nitrogen Dioxide
Dinitrogen Trioxide
Dinitrogen Pentoxide
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Assignment

• Worksheet
• Naming and Writing Molecular Compounds Using
  Prefixes

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Section 1 Compounds with Polyatomic Ions

• Many compounds are composed of polyatomic ions (a
  group of covalently bonded atoms that carry a
  charge).
• Examples of polyatomic ions
• Sulfate (SO4)2-
• Nitrate (NO3)
• Phosphate (PO4)3-
• Carbonate (CO3)2-
• Dichromate (Cr2O7)2-
• Ammonium (NH4)

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Section 1 Compounds with Polyatomic Ions

• Most polyatomic ions end with ate or -ite
  but there are a few exceptions
• Cyanide (CN)-
• Hydroxide (OH)-
• Note of caution
• Dont confuse these with binary compounds since
  they end in ide.

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Section 1 Naming Compounds with Polyatomic Ions

• Simply write the complete name of the positive
  element and the name of the polyatomic ion.
• KNO3 Potassium Nitrate
• CaSO4 Calcium Sulfate
• Al(OH)3 Aluminum Hydroxide

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Section 1 Writing Compounds with Polyatomic
Ions

• Writing the formulas for these compounds are a
  little trickier.
• Make sure that you treat the polyatomic ion as a
  whole unit and do not change its subscripts!
• (SO4)2- 1 sulfate ion
• (SO4)2-2 2 sulfate ions NOT
• (S2O8)

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Section 1 Writing Compounds with Polyatomic
Ions

• Examples
• Potassium nitrate

Totals 1 and 1- 0
Charges -
Symbols K (NO3)
Final Formula KNO3 (no parenthesis needed
since only 1 ion is required
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Section 1 Writing Compounds with Polyatomic
Ions

• Examples
• Aluminum Sulfate

Totals 6 and 6- 0
Charges 3 2-
Symbols Al (SO4)
Add Subscripts 2 3
Final Formula Al2(SO4)3 (parenthesis must be
used to show 3 sulfate ions)
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Section 1 Writing Compounds with Polyatomic
Ions

• Polyatomic ions may be paired with transition
  metals that have multiple charges.
• Ex Copper (II) and sulfate CuSO4
• But Copper (I) and sulfate Cu2SO4
• When naming them the Roman numeral must be
  included.
• Fe3(PO4)2 Iron (II) Phosphate

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Assignment

• Worksheet
• Naming and Writing Formulas for Compounds
  Containing Polyatomic Ions

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Section 1 Naming Acids and Salts

• Memorize the formulas for the common acids.
• All begin with one or more H atoms.
• Sulfuric Acid H2SO4
• Hydrochloric Acid HCl
• Nitric Acid HNO3
• Phosphoric Acid H3PO4
• Carbonic Acid H2CO3

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Section 1 Naming Acids and Salts

• Binary acids contain only 2 elements
• Example Hydrochloric acid HCl
• Oxyacids contain hydrogen, oxygen, and one other
  element
• Example Sulfuric acid H2SO4

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Section 1 Naming Acids and Salts

• When acids have less oxygen atoms than normal the
  names change
• Normal HClO3 is chloric acid
• Loss of 1 oxygen atom HClO2 is chlorous acid
• Loss of 2 oxygen atoms HClO is hypochlorous acid
• An extra oxygen atom HClO4 is perchloric acid

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Section 1 Naming Salts

• Any ionic compound composed of a cation and the
  anion from an acid is referred to as a salt.
• Example
• NaCl (anion from hydrochloric acid)
• CaSO4 (anion from sulfuric acid)

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Section 2

• Oxidation Numbers

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Section 2 Oxidation Numbers

• Oxidation numbers are numbers assigned to the
  atoms in a molecular compound or ion that
  indicates the general distribution of electrons
  among bonded atoms.
• Oxidation numbers are not actual charges.
• Oxidation numbers are useful in naming compounds
  and writing formulas.

-1
1
2
-2
3
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Section 2 Oxidation Numbers

• Rules for assigning oxidation numbers
• Atoms in a pure element have an oxidation number
  of zero O2 Ox. 0
• Fluorine always has ox. of -1
• Oxygen almost always has ox. of -2 except in
  peroxides such as H2O2 then it is a -1.

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Section 2 Oxidation Numbers

• (Rules continued)
• Hydrogens ox. is 1 unless it is with metals
  then it is -1
• The sum of the ox. in molecules must be zero,
  but in polyatomic ions, it is equal to the ions
  charge.

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Section 2 Oxidation Numbers

• What are the oxidation numbers for each atom in
  these compounds?
• UF6 Fluorine is -1 x 6 -6
• Uranium 6 6 (-6) 0
• H2SO4 Oxygen is -2 (x 4 -8)
• Hydrogen is 1 (x 2 2) so
• Sulfur has to be 6
• (6) (2) (-8) 0

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Section 2 Oxidation Numbers

• What are the oxidation numbers for the chlorate
  polyatomic ion?
• ClO3- Oxygen is -2 x 3 -6
• Chlorine must be 5
• (5) (-6) -1 (the ions charge)

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Section 2 Oxidation Numbers

• Assignment
• Page 219, question 1, A-K

41
Section 3

• Using Chemical Formulas

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Section 3 Using Chemical Formulas

• With a chemical formula, you can calculate many
  characteristic values for a compound.
• Formula Mass
• Compounds have masses just like elements.

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Section 3 Using Chemical Formulas

• Formula Mass
• The formula mass of any molecule, formula unit,
  or ion is the sum of the average atomic masses of
  all the atoms represented in its formula.
• To find the mass of a compound simply add the
  masses of the atoms that make up the compound.
  Units are amus.

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Section 3 Using Chemical Formulas

• To find the formula mass of sulfuric acid
  (H2SO4)
• element of atoms x mass (to 2 decimals)
• H 2 1.01 2.02 amu
• S 1 32.0132.01 amu
• O 4 16.0064.00 amu
• 98.03 amu

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Section 3 Using Chemical Formulas

• To find the formula mass of Calcium Nitrate
  Ca(NO3)2
• element of atoms x mass
• Ca 1 40.08 40.08 amu
• N 2 14.01 28.02 amu
• O 6 16.00 96.00 amu
• 164.10 amu

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Section 3 Using Chemical Formulas

• Molar Mass
• The mass of a mole of any substance is equal to
  its formula mass except instead of amus it is
  in grams.
• Formula mass of sulfuric acid 98.03 amu
• Molar mass of sulfuric acid 98.03 grams

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Percentage Composition

• It is sometimes useful to know what the
  percentage of a compound is an element.
• What percentage of water is oxygen?

H 1.01 x 2 2.02 O 16.0 x 1 16.0 Molar
Mass 18.02 g
16.0 18.02 88.79
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Section 3 Using Chemical Formulas

• Molar Mass can be used as a conversion factor.

98.03 grams
1 mole H2SO4
or
98.03 grams
1 mole H2SO4
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Section 3 Using Chemical Formulas

• How many moles are there in 25 g of H2SO4?

1 mole H2SO4
25 g H2SO4
x

0.255 mol
98.03 grams
50
Section 3 Using Chemical Formulas

• What is the mass of 4.2 moles of H2SO4?

98.03 g H2SO4
4.2 mol H2SO4
x

411.73 mol
1 mol H2SO4
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Section 3 Using Chemical Formulas

• How many molecules are in 54 g of H2SO4?

6.02 x 1023 molecules H2SO4
54 g H2SO4

x
98.03 g H2SO4
3.32 x 1023 molecules
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Section 4

• Determining
• Chemical Formulas