Transcript Chemical Formulas and Chemical Compounds

Chemical Formulas
and
Chemical Compounds
Chapter 7
Systematic Naming
• There are too many compounds to
remember the names of them all.
• Compound is made of two or more
elements.
• Name should tell us how many and
what type of atoms.
Significance of a Chemical Formula
Molecular formulas
• Number of atoms of each element in one
molecule of a compound
• C2H6 = ethane (2 carbon atoms, 6 hydrogen
atoms)
• Ionic Compounds
• Represents the simplest whole number
ratio of the compounds cations and anions
• Al2(SO4)3 = aluminum sulfate (2 aluminum
ions, 3 sulfate ions)
•
Charges on ions
• For most of Group A elements,
location on the Periodic Table can
tell what kind of ion they form
• Elements in the same group have
similar properties.
• Including the charge when they
are ions.
Charge in groups 1A, 2A and 3A
is the group number
1+
2+
3+
3- 2- 1-
Naming Monatomic Ions
• 1. Monatomic cations
• Identified by the element’s name
• 2. Monatomic anions
• Drop the ending of the element
name
• Add an “–ide” ending
Name these
Na1+
2+
Ca
3+
Al
Sodium ion
Calcium ion
Aluminum ion
Li1+
Lithium ion
Write Formulas for these
Potassium
ion
Magnesium
Copper(II)
ion
ion
K1+
2+
Mg
2+
Cu
6+
Cr
Chromium(VI) ion
ion
2+
Ba
Mercury(II)
2+
Hg
Barium
ion
Name these
Cl1-
N3Br1O2Ga3+
Chloride ion
Nitride ion
Bromide ion
Oxide ion
Gallium ion
Write these
Sulfide
Iodide
ion
ion
S2I1-
Phosphide
ion P3-
Strontium
ion Sr2+
Day 2
Binary Ionic Compounds
• Binary Compounds
• Compounds composed of
two different elements
• Binary ionic cmpd, total #
of positive and negative
charges must equal
Writing Formulas for Binary Ionic
Compounds
• Write the symbols for the ions side
by side. ALWAYS write the cation
first!
Al3+ O2-
• Cross over the charges by using the
absolute value of each ion’s charge
as the subscript for the other ion
Al23+ O32-
• Check that the subscripts are in
smallest whole number ratio
Al2O3
Naming Binary Ionic
Compounds
Al2O3
• 1. Name the cation(don’t
change) Aluminum
• 2. Name the anion (drop
add-ide) Oxide
Aluminum Oxide
Section 1 Chemical Names and
Formulas
Naming Ionic Compounds
Click below to watch the Visual Concept.
Visual Concept
The Stock System of Nomenclature
• Most transition metals can
have more than one type of
charge.
• Indicate the charge with
Roman numerals in
parenthesis.
• Fe2+Iron(II)
• Fe3+ Iron(III)
• Roman numerals are never
used:
• For anions
• For metals that form
only one ion
Co2+
Cobalt(II) ion
CuCl2
Copper(II) chloride
Naming ions Cont…..
• A few, like silver, zinc and
cadmium only form one kind of
ion
• Don’t get roman numerals
• Ag+ silver ion
• Zn2+ zinc ion
• Cd2+ cadmium ion
Compounds Containing Polyatomic
Ions
• Naming a series of similar polyatomic ions
• NO2NO3• Nitrite Nitrate
• Most common ion is given –ate ending, ion
with one less oxygen –ite
• Pg 214
• Naming compounds containing polyatomic ions
• Same as for monatomic ions
Day 3
Molecular Nomenclature
• Prefix System (binary compounds)
1. Less e-neg atom
comes first.
2. Add prefixes to indicate # of atoms.
Omit mono- prefix on first element.
3. Change the ending of the
second element to -ide.
C. Molecular Nomenclature
PREFIX
monoditritetrapentahexaheptaoctanonadeca-
NUMBER
1
2
3
4
5
6
7
8
9
10
Molecular Nomenclature
CCl4
carbon tetrachloride
N 2O
dinitrogen monoxide
SF6
sulfur hexafluoride
Molecular Nomenclature
arsenic trichloride
AsCl3
dinitrogen pentoxide
N 2O 5
tetraphosphorus decoxide
P4O10
Day 4
Oxidation Numbers
• also known as the oxidation state
• is a simple record-keeping concept, to help in
remembering of formulas and chemical
phenomena
• also allow for easy classification and naming of
new compounds
• Rules see pg 220
Section 2 Oxidation Numbers
Rules for Assigning Oxidation
Numbers
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Visual Concept
Day 5
Percent Composition
• the percentage by mass of each
element in a compound
mass of element
% compositio n 
 100
total mass
Section 3 Using Chemical Formulas
Percentage Composition
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Visual Concept
Percentage Composition
• Find the % composition of Cu2S.
%Cu =
%S =
127.10 g Cu
 100 =
159.17 g Cu2S
79.852% Cu
32.07 g S
159.17 g Cu2S
 100 =
20.15% S
Percent Composition
• Find the percentage composition
of a sample that is 28 g Fe and
8.0 g O.
%Fe =
%O =
28 g
36 g
8.0 g
36 g
 100 = 78% Fe
 100 = 22% O
Percentage Composition
• How many grams of copper are in
a 38.0-gram sample of Cu2S?
Cu2S is 79.852% Cu
(38.0 g Cu2S)(0.79852) = 30.3 g Cu
Percent Composition
• Find the mass percentage of
water in calcium chloride
dihydrate, CaCl2•2H2O?
%H2O =
36.04 g
 100 = 24.51%
H2O
147.02 g
Using Chemical Formulas
• Formulas mass-sum of all the average atomic
masses of all the atoms in the formula
• H2O =18.02 amu
• A compound’s formula mass is equal to
compounds molar mass
• H2O =
• 2 Moles of Hydrogen 1 mole of Oxygen
• 18.02 g/mol
Empirical Formula
• Smallest whole number ratio of
atoms in a compound
C 2H 6
reduce subscripts
CH3
Empirical Formula
1. Find mass (or %) of each element.
2. Find moles of each element.
3. Divide moles by the smallest # to
find subscripts.
4. When necessary, multiply
subscripts by 2, 3, or 4 to get
whole #’s.
Empirical Formula
Find the empirical formula for a
sample of 25.9% N and 74.1% O.
25.9 g 1 mol
= 1.85 mol N
=1N
1.85 mol
14.01 g
74.1 g 1 mol
= 4.63 mol O
= 2.5 O
16.00 g
1.85 mol
Empirical Formula
N1O2.5
Need to make the subscripts whole
numbers  multiply by 2
N2O5
Molecular Formula
• “True Formula” - the actual
number of atoms in a compound
empirical
formula
CH3
?
molecular
formula
C2H6
Molecular Formula
1.
Find the empirical formula.
2. Find the empirical formula mass.
3. Divide the molecular mass by the
empirical mass.
4. Multiply each subscript by the
answer from step 3.
MF mass
n
EF mass
EF n
Molecular Formula
• The empirical formula for ethylene
is CH2. Find the molecular formula if
the molecular mass is
28.1 g/mol?
empirical mass = 14.03 g/mol
28.1 g/mol
14.03 g/mol
= 2.00
(CH2)2  C2H4
Section 4 Determining Chemical
Formulas
Comparing Molecular and Empirical
Formulas
Click below to watch the Visual Concept.
Visual Concept