Accelerated ChemistryChapter 7 Note PacketMr. Seidel
(student edition)
Chapter 7 problems: 1, 3, 6-8, 10, 11, 13, 17, 24, 25, 29, 33, 36, 42, 50
Check out the blue problems in this chapter – they really show how to do all the work you need to know how to do! Also check out the tables and figures – they help!
7.1 Chemical Names and Formulas
Lots of common names:dry ice
epsom salts
milk of magnesia
chemical formulas show the relative #’s of atoms in a chemical compound
ex.C12H22O11Pb(NO3)4(NH4)2CrO4
monatomic ions – end in “ide” – look up charges on periodic table
compare F ()to F-1
compare S ()to S-2
Writing Formulas for Ionic Compounds
positive ions - cationsnegative ions - anionscharges must = 0
Binary ionic compounds
3 rules(2 for now) - if the charges on the ions are the same, “drop ‘em”
- if the charges are different, “criss cross” (apple sauce?)
charges the same -
charges different
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Ternary Ionic compounds
polyatomic ions - if you take, a polyatomic ion, more than once, use parentheses...... fool!
Naming Ionic Compoundsname front (positive), name back (negative)
binary ionic compounds - composed of only two types of elements
NaClMgCl2
Al2O3NaH
“The big lie” - transition metals aren’t always + 2
ex-CuClCu = +1chloride
CuCl2Cu = +2chloride
new system - Stock System - used for naming compounds with metals that have multiple charges
ternary compounds - 3 or more elements make up the compound
ex MgCO3
Fe(NO3)3
notable exceptions -
room for some more practice:
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Naming Molecular Compoundsmolecular = covalent
we use prefixes ** prefixes can only be used with covalent compounds
1 =2 = 3 =4 =5 =6 =
don’t use the prefix on the first atom
examples:CO, CO2, PCl3, CBr4, N2O5, SF6
Naming Acids – we’ll do this later in chapter 16
7.2Oxidation numbers - since electrons are shared, there is no definite charge - we assign the more electronegative element the “apparent” negative charge- this is known as the oxidation # - oxidation numbers can also be positive.
oxidation # -
rules for assigning oxidation #’s
1. Free elements =ex - 2. Oxidation #’s of ions =ex -
3. F = 4. 0 = (usually - peroxides O = )
5. H = (usually - except in metal hydrides) 6. more electronegative atom gets a ( ) charge
7. Ox #’s add up to in compounds 8. Ox #’s = the in polyatomic ions
examples: FeO, Fe2O3, H2SO4, H2SO3, H2Cr2O7, NO3-1, NO2-1
7.3Using Chemical Formulas
Step 1 – be able to calculate molar mass (aka – formula mass, molecular weight, atomic weight, atomic mass, gram formula weight, etc.)
Add atomic weights from the periodic table – round to the nearest 10th place
ex. CH4 =
don’t forget hydrates! MgSO4. 7 H20 =
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Step 2 – be able to convert between grams, moles, particles, and liters
Mole Relationships - For starters in chemistry, we have to be able to convert between moles, grams, and molecules/atoms of substance (also liters when we work with gases)
use the“mole map
_____ mole
_____ atom/molecule
_____ gram
_____ liter (at STP)
convert 32.0 g of CH4 to moles,liters, molecules, total atoms, atoms of H
Percentage Composition - every compound has a certain percentage of each type of atom
(we measure it by mass)
% composition =
ex 1 - calculate % composition if a compound contains 24 g of Carbon and 64 g of Oxygen
ex 2 - what is the percentage composition of Ba(OH)2
7.4Determining a compound’s empirical and molecular formula
empirical formula - the lowest whole number ratio of atoms in a compound (simplest formula)
3 basic types of problems - first, three rules
1. Divide (%’s or grams) by the gram atomic mass
2. Divide the resulting #’s by the smallest of those numbers
3. Multiply by 2 or 3 only if a whole number ratio isn’t the result of step 2
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example 1 - calculate the empirical formula if there is 52.17 % C, 13.04% H, and 34.78 % O
example 2 - calculate the empirical formula is there is 26.56 % K, 35.41 % Cr, and 38.03 % O
example 3 - Find the empirical formula if a sample contains 5.6 g N and 12.8 g O
Finding Molecular Formula - the same steps as empirical formula with one additional step - use the gram formula mass of the empirical formula and its relationship to the gram formula mass of the molecular formula to find what number to multiply the empirical formula by to find the molecular formula (sounds more complicated than it is)
example 5 - Find the molecular formula of a compound (mw = 144.0 g) with 66.67 % C,
11.11 % H, and 22.22 % O
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