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Chapter 7. Chemical Formulas and Chemical Compounds. Section 1: Chemical Names & Formulas. There are literally thousands of chemicals Isn’t always best to use common names for chemicals (calcium carbonate is limestone , sodium chloride is salt , and hydrogen oxide is water )

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chapter 7

Chapter 7

Chemical Formulas and

Chemical Compounds

section 1 chemical names formulas
Section 1: Chemical Names & Formulas
  • There are literally thousands of chemicals
  • Isn’t always best to use common names for chemicals (calcium carbonate is limestone, sodium chloride is salt, and hydrogen oxide is water)
  • Common names don’t give information about chemical composition.
section 1 chemical names formulas3
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
section 1 chemical names formulas4
Section 1: Chemical Names & Formulas
  • When parentheses are used you must multiply inside and out.
    • Al2(SO4)3

(2 Aluminums, 3 Sulfurs, 12 Oxygens)

section 1 names of binary compounds
Section 1: Names of Binary Compounds
  • Binary compoundsare 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)
section 1 formulas of binary compounds
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
section 1 formulas of binary compounds7
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

section 1 formulas of binary compounds8
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.
assignment
Assignment:
  • Worksheet: Writing formulas and names for binary compounds.
section 1 stock system of nomenclature
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: Pb+3 and Pb+4

Tin: Sn+2 and Sn+4

section 1 stock system of nomenclature11
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: FeOFe2O3
section 1 stock system of nomenclature12
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

section 1 stock system of nomenclature13
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???
section 1 stock system of nomenclature14
Section 1: Stock System of Nomenclature

Cu Br2

Then +1 -2 ≠ 0

If charges are +1 -1

section 1 stock system of nomenclature15
Section 1: Stock System of Nomenclature

Cu Br2

Then +2 -2 = 0

If charges are +2 -1

assignment16
Assignment
  • Worksheet:

Naming and Writing Formulas for Compounds Using the Stock System

section 1 naming binary molecular compounds
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
section 1 naming binary molecular compounds18
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.
section 1 naming binary molecular compounds19
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 atoms:Deca
section 1 naming binary molecular compounds20
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

assignment21
Assignment
  • Worksheet:

Naming and Writing Molecular Compounds Using Prefixes

section 1 compounds with polyatomic ions
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)+
section 1 compounds with polyatomic ions23
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:

Don’t confuse these with binary compounds since they end in “ide.”

section 1 naming compounds with polyatomic ions
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
section 1 writing compounds with polyatomic ions
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)

section 1 writing compounds with polyatomic ions26
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

section 1 writing compounds with polyatomic ions27
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)

section 1 writing compounds with polyatomic ions28
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
assignment29
Assignment:
  • Worksheet:

Naming and Writing Formulas for Compounds Containing Polyatomic Ions

section 1 naming acids and salts
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
section 1 naming acids and salts31
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
section 1 naming acids and salts32
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
section 1 naming salts
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)
section 2
Section 2

Oxidation Numbers

section 2 oxidation numbers
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

section 2 oxidation numbers36
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.
section 2 oxidation numbers37
Section 2: Oxidation Numbers
  • (Rules continued):
    • Hydrogen’s 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.
section 2 oxidation numbers38
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

section 2 oxidation numbers39
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 ion’s charge)

section 2 oxidation numbers40
Section 2: Oxidation Numbers
  • Assignment:
    • Page 219, question 1, A-K
section 3
Section 3:

Using Chemical Formulas

section 3 using chemical formulas
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.
section 3 using chemical formulas43
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 amu’s.
section 3 using chemical formulas44
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 32.01=32.01 amu

O 4 16.00=64.00 amu

98.03 amu

section 3 using chemical formulas45
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

section 3 using chemical formulas46
Section 3: Using Chemical Formulas
  • Molar Mass
    • The mass of a mole of any substance is equal to its formula mass – except instead of amu’s it is in grams.
    • Formula mass of sulfuric acid = 98.03 amu
    • Molar mass of sulfuric acid = 98.03 grams
percentage composition
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%

section 3 using chemical formulas48
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

section 3 using chemical formulas49
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

section 3 using chemical formulas50
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

section 3 using chemical formulas51
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

section 4
Section 4

Determining

Chemical Formulas