Unit 7: Chemical Formulas and Compounds Guided Notes
I.
Ch. 7.1: Naming Ionic Compounds
A.
B.
Warm Up:
1.
Distinguish between a cation and an anion.
2.
Which elements tend to form cations? anions?
3.
Using a periodic table, predict the charge ion each of the following elements form:
calcium
c) sulfur
b)
fluorine
d) aluminum
Writing Formulas and Naming Chemical Compounds
1.
C.
a)
There are two types of chemical compounds:
a)
ionic compounds
b)
covalent (molecular) compounds
Ionic Compounds are composed of a cation and an anion.
1.
cations – positively charged ion (_______________)
2.
anions – negatively charged ion (__________________)
3.
Monoatomic Ions
a)
b)
Cations
(1)
For monatomic cations, the name of the ion is the name of the element.
(2)
examples:
(a)
Na+ = ________________________
(b)
Mg2+ = ________________________
(c)
Al3+ = ________________________
Some metals are able to form more than one stable ion (___________________)
(1)
usually transition elements
(2)
example: _________________
(3)
forms Cu2+ and Cu+
(4)
use Roman numerals to distinguish charge
(5)
copper (II) and copper (I)
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c)
Anions
(1)
Monoatomic anions are named by dropping the ending of the element and
replacing with the suffix “___________”.
(2)
D.
examples:
(a)
Cl- = ________________________
(b)
O2- = ________________________
(c)
N3- = ________________________
Naming Binary Ionic Compounds
1.
The nomenclature, or naming system, or binary ionic compounds involves combining the names
of the compound’s positive and negative ions.
2.
The name of the cation is given first, followed by the name of the anion:
a)
E.
Al2O3-
Independent practice
1.
What is the formula and name for Sodium and Oxygen?
2.
What would the formula and name be for potassium and sulfur?
F.
The Stock System of Nomenclature (look above to 3b.)
G.
Independent Practice
1.
Give the formula for Chromium (II) Fluoride
2.
What is the name of Fe2O3?
H.
Compounds Containing Polyatomic Ions (See D1.)
I.
Give the formula for…
1.
Potassium Chlorate
2.
Hydrogen Sulfite
3.
Tin(IV) sulfate
2
II.
Ch. 7.2: Naming Covalent Compounds
A.
Warm up:
1.
Give the Lewis Structure for the following molecules
a)
CCl4
b)
CO
c)
CO2
B.
Unlike ionic compounds, molecular compounds are composed of individual covalently bonded
units, or molecules.
1.
The old system (prefix) of naming molecular compounds is based on the use of prefixes.
a)
Prefix
C.
examples:
(1)
CCl4 — carbon tetrachloride (tetra- = 4)
(2)
CO — carbon monoxide (mon- = 1)
(3)
CO2 — carbon dioxide (di- = 2)
Number of Atoms
Example
1
CO
2
SiO2
3
SO3
4
SCl4
5
SbCl5
6
CeB6
7
IF7
8
Np3O8
9
I4O9
10
S2F10
Name
Independent Practice
1.
Give the name for As2O5.
2.
Write the formula for oxygen difluoride.
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III.
Ch. 7.3: Acids, Salts, and Oxidation Numbers
A.
Warm Up
1.
B.
Give the name for the following compounds
a)
NaF
c) SiO2
b)
CaCl2
d) N2O5
Acids and Salts
1.
An acid is a certain type of molecular compound. Most acids used in the laboratory are either
binary acids or oxyacids.
2.
Binary acids are acids that consist of two elements, usually hydrogen and a halogen.
3.
Oxyacids are acids that contain hydrogen, oxygen, and a third element (usually a nonmetal).
4.
In the laboratory, the term acid usually refers to a solution in water of an acid compound rather
than the acid itself.
a)
example: hydrochloric acid refers to a water solution of the molecular compound
hydrogen chloride, HCl
5.
Many polyatomic ions are produced by the loss of hydrogen ions from oxyacids.
a)
6.
salt.
examples:
Acid name
Acid formula
Ion
(1)
sulfuric acid
H2SO4
sulfate
(2)
nitric acid
HNO3
nitrate
(3)
phosphoric acid
H3PO4
phosphate
An ionic compound composed of a cation and the anion from an acid is often referred to as a
a)
examples:
(1)
Table salt, NaCl, contains the anion from hydrochloric acid, HCl.
(2)
Calcium sulfate, CaSO4, is a salt containing the anion from sulfuric acid, H2SO4.
(3)
The bicarbonate ion, HCO3-, comes from carbonic acid, H2CO3.
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C.
Oxidation Numbers
1.
In order to indicate the general distribution of electrons among the bonded atoms in a
compound or a polyatomic ion, oxidation numbers are assigned to the atoms composing the compound
or ion.
2.
Unlike ionic charges, oxidation numbers do not have an exact physical meaning: rather, they
serve as useful “bookkeeping” devices to help keep track of electrons.
3.
Rules for Assigning Oxidation Numbers
a)
In general when assigning oxidation numbers, shared electrons are assumed to “belong”
to the more electronegative atom in each bond.
(1)
All free elements (not combined with other elements) have an oxidation
number of zero.
(2)
Ions in ionic bonds have an oxidation number equal to charge
(a)
+2
- alkali metals have an ox. number of +1, alkaline have an ox. number of
(3)
Oxygen is always -2 (except in a peroxide or when bonded to F)
(4)
Hydrogen is usually +1 (except when it's bonded to a metal--> usually -1)
(a)
(5)
Ex: LiH
Fluorine is always -1
(a)
Halogens (Cl, Br, I) are generally -1, unless bonded to Oxygen, then they
are positive.
(6)
In a compound all oxidation numbers add up to 0, in a polyatomic ion (SO4) they
add up to the overall charge.
4.
IV.
Oxidation Numbers Practice
a)
PCl3
d) NO
b)
PCl5
e) Mo2O3
c)
N2O
Ch. 7.4: Calculations with Chemical Formulas
A.
B.
Warm Up: give the oxidation numbers for the following atoms
1.
NaPO4
2.
HClO3
3.
C6H12O6
Formula Mass (Molar Mass)
1.
sum of the atomic masses of all atoms represented in its formula
5
C.
D.
2.
label for formula mass is atomic mass units (amu)
3.
Determine the formula mass for the following compounds.
CO2
b)
Mg(C2H3O2)2
Percentage Composition
1.
To find the mass percentage of an element in a compound, the following equation can be used:
2.
The mass percentage of an element in a compound is the same regardless of the sample’s size.
Percent Composition from the Chemical Formula
1.
E.
a)
Calculate the percent composition of each element in the following compounds.
a)
C in CO2
b)
O in Mg(C2H3O2)2
Percent Composition from Mass Data (backwards)
1.
When a 13.60 gram sample of magnesium oxide is decomposed, 5.40 g of oxygen is obtained.
What is the percentage composition of each element in this compound?
V.
Ch. 7.5 Determining the Empirical Formula of a Compound
A.
Warm up:
1.
A compound consists of potassium and oxygen. What is the formula for this compound?
2.
A sample of a compound is found to contain 6.35 g iron and 3.65 g sulfur . Express the amount
of each element in terms of moles.
3.
Other than they contain the same elements, what do the compounds C3H6 and C5H10 have in
common?
B.
If we know how much of each element is present in a compound, we can determine the
formula of the compound.
1.
Amounts may be expressed in:
a)
____________________________
b)
____________________________
c)
____________________________
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C.
If composition is given in terms of percentages, assume you have a ________ g sample of the
compound
D.
From this data, the _______________________ can be determined.
1.
The empirical formula or _________________ formula is a formula in which the elements are in
their lowest whole number ratio.
2.
The empirical formula may or may not be the _______________ formula.
a)
Example:
(1)
The formula for glucose is ___________________.
(2)
Its empirical formula for is __________________.
3.
The subscripts in a chemical formula represent a ______________ ratio of elements in the
compound.
E.
Practice:
1.
Example #1: Analysis shows a compound consists of 32.4% Na, 22.6% S, and 45.0% O.
Determine the empirical formula for this compound.
2.
Example #2: A compound is found to contain 4.43 g phosphorus and 5.72 g oxygen. Find the
empirical formula for this compound.
F.
Independent Practice
1.
Determine the empirical formula of each of the followings compounds if a sample contains
a)
0.104 mol K, 0.052 mol C, and 0.156 mol O
b)
5.28 g Sn and 3.37 g F
c)
36.8% N and 63.2% O
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VI.
Ch. 7.6 Determining Molecular Formulas
A.
Warm Up: Give the empirical formula for the following
1) What’s the empirical formula of a molecule containing 65.5% carbon, 5.5% hydrogen, and 29.0%
oxygen?
2) What’s the empirical formula of a molecule containing 18.7% lithium, 16.3% carbon, and 65.0%
oxygen?
B.
C.
D.
Molecular Formula – actual formula
1.
Actual formula is a multiple of the empirical formula.
2.
C6H12O6 = 6 (CH2O)
In order to find the molecular formula you must be given the formula mass of the compound.
1.
Compare the empirical mass to the formula mass. This will give you the multiple.
2.
Formula mass / empirical mass= multiplier
DETERMINING THE MOLECULAR FORMULA OF A COMPOUND
1.
Example #1: Determine the molecular formula of a compound with an empirical formula of CH
and a formula mass of 78 amu.
2.
Example #2: A compound with a formula mass of 60.0 amu is found to be 39.9% carbon, 6.7%
hydrogen, and 53.4% oxygen by mass. Find its molecular formula.
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