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CHE 111 - Module 3
CHAPTER 3
LECTURE NOTES
STOICHIOMETRY
• Stoichiometry is the study of the quantitative relationships between the amounts of reactants and products in chemical reactions.
• We use BALANCED equations to understand stoichiometric relationships of the elements and compounds within a chemical reaction.
The Balanced Equation
2Al(s) + 3Br2(l) Al2Br6(s)
2mol of Al : 3mol of Br2 : 1mol of Al2Br6
Therefore the ratio of Al to Br2 to Al2Br6
is 2:3:1 for the chemical reaction to occur.
A Closer Look at the Equation
2Al(s) + 3Br2(l) Al2Br6(s)
• The chemicals on the left are the reactants and the right are the products.
• The coefficient in front of the chemical denotes the stoichiometric relationship.
Numerical Subscripts
2Al(s) + 3Br2(l) Al2Br6(s)
• The numerical subscript represents the
number of atoms present in the molecule
– ex. Br2 means that an atom of Br is bonded to another atom of Br
– Therefore: Br-Br = Br2
Denoting the Phase of Matter
Phase of Matter Symbol
Solid (s)
Liquid (l)
Gas (g)
Aqueous (aq)
2Al(s) + 3Br2(l) Al2Br6(s)
The subscript letters in parenthesis denote the phase of matter that the chemical is in.
Formulas and Models of Ethanol
• Molecular Formulas C2H6O
• Condensed Formulas C2H5OH
H H
• Structural Formulas H-C-C-O-H
H H
• Molecular Models (classroom models)
Molecular Models
• Cache program - models - organic models - ethanol
• CD-ROM screen 3.4
• Model of ice
Ions and Ionic Compounds
• Ions are atoms or groups of atoms that have lost or gained electrons resulting in an overall positive or negative charges.
• Ionic compounds are compounds formed by the combination of (+) and (-) ions.
(+) ions are called cations(-) ions are called anions
Formation of Ions
Formation of a cation by a loss of electrons
Li atom Li+ + 1 e- released
(3p and 3e-) (3p and 2e-)
Formation of an anion by gaining electrons
F atom + 1 e- added F
(9p and 9e-) (9p and 10e-)
Ions and the Periodic Table
Family 1A 2A 3A 4A 5A 6A 7A 8A
IonicCharge
+1 +2 +3 -3 -2 -1
Metals of group 1A, 2A & 3A form+1, +2, and +3 ions; and non-metalsof group 5A, 6A, and 7A form -3, -2,and -1 respectively.
Polyatomic Ions
• Table 3.1 - page 89
• CD-ROM Screen 3.6
• Hand out
• Flash Cards
Common Polyatomic Ions
• carbonate ion CO3-2
• sulfate ion SO4-2
• sulfite ion SO3-2
• hydroxide OH-
• phosphate PO4-3
• permanganate MnO4-
• chromate CrO4-2
• dichromate Cr2O7-2
• ammonium NH4+
• oxalate C2O4-2
• bicarbonate HCO3-
• cyanide ion CN-
• acetate C2H3O2-
• peroxide O2-2
• thiosulfate S2O3-2
• bisulfite HSO3-
Oxoanions
A polyatomic anion containing oxygen is called an oxoanion and is named as follows:
• Greater # of O atoms has the suffix -ate.
• Lesser # of O atoms has the suffix -ite.
Ex.NO3
- is called nitrate ion
NO2- is called nitrite ion
Naming Oxoanions
More than 2 ions in an oxoanion grouping
are named as follows:
• Largest # of O atoms has a prefix of per- and a suffix of -ate
• Next larger # of O atoms has a suffix -ate
• Smaller # of O atoms has a suffix -ite
• Smallest # of O atoms has a prefix of hypo- and a suffix of -ite
Naming Oxoanions
Ex.
ClO4- is called perchlorate
ClO3- is called chlorate
ClO2- is called chlorite
ClO- is called hypochlorite
Ionic Compounds
Ca+2 + 2Cl- CaCl2
Each ion comes together based on charge to form an overall neutral ionic compound.
3Ca+2 + 2PO4-3 Ca3(PO4)2
The cation and the polyatomic ion come together based on charge to form an overall neutral ionic compound.
Naming Ionic Compounds
• Naming Positive Ions – Cations• Cations are named first in the compound
and as follows:– Monatomic cations are mostly metals and are
named directly as they are on the periodic table.– Transition metals are named according to their
ionic charge– Polyatomic cation, NH4
+ is named ammonium directly
Naming Ionic Compounds
• Naming Negative Ions – Anions
• Anions are named lastly and have specific naming rules as follows:– Monatomic ions are named with an –ide after
its atomic name– Polyatomic ions are named as memorized
dropping the word ion.
Cr +2 Cr +3 Cr +6 Chromium II,III&VI
Mn +2 Mn +3 Mn +4 Mn +6 Mn +7
Fe +2 Fe +3 Fe +6 Iron II, III & VI
Co +2 Co +3 Cobalt II & III
Ni +2 Ni +3 Nickel II & III
Cu +1 Cu +2 Copper I & II
Pb +2 Pb +4 Lead II & IV
Sn +2 Sn +4 Tin II & IV
Au +1 Au +3 Gold I & III
Hg +1 Hg +2 Mercury I & II
Zn +2 Zinc
Ag +1 Silver
Naming Molecular Compounds
• 1 mono• 2 di• 3 tri• 4 tetra• 5 penta• 6 hexa• 7 hepta• 8 octa
Formula & Molecular Weights
• Review of spectra lab - MW calculations
• CD-ROM Screen 3.14
• Definition: The total mass of the formula unit or molecule with consideration to the mass of each component element that makes up the overall unit.
Calculating Formula & MW
• Remember we said that:
1 mole C = 12.011g C = 6.02x1023 atoms C
• If we add up the number atoms present of each element in a molecule or formula unit and multiply each by its atomic weight on the periodic table,
• Then the resultant sum of each element added together will give you the formula or molecular weight.
Example of MW Calculation
• Determine the MW of H20
– 1 O @ 15.999g/mole– 2 H @ 1.008g/mole
• Therefore 2 x 1.008 = 2.016g/mole
• and 1 x 15.999 = 15.999g/mole
Total molar mass = 18.015g/mole
Determine the MW of ethanol: C2H5OH
Converting Mass to Moles
• Question: How many moles of H2O are in 42.0g of water?
• Answer: First you determine the MW of water as we did on the previous slide, then you convert
42.0g H2O x 1 mole H2O =
18.016g H2O
Percent Composition
• Calculate the percent composition of NH3
– First determine the atomic weights of each N and H from the periodic table
– Then calculate the MW of the ammonia molecule
– Take the mass of each element and divide by the MW and multiply 100%
• CD-ROM Screens 3.14 and 3.16
Hydrated Compounds
• Definition: Ionic compound that has water molecules incorporated within its crystal structure
• Ex. CuCl2•2H2O
– Where we name this compound copper(II) chloride dihydrate
– When calculating MW, we calculate the two waters into the overall mass of the compound