Title: Chapter 5 Molecules and Compounds
1Chapter 5Molecules andCompounds
2Molecules and Compounds
- Salt
- Sodium shiny, reactive, poisonous
- Chlorine pale yellow gas, reactive, poisonous
- Sodium chloride table salt
- Sugar
- Carbon pencil or diamonds
- Hydrogen flammable gas
- Oxygen a gas in air
- Combine to form white crystalline sugar
3Law of Constant Composition
- all pure substances have constant composition
- all samples of a pure substance contain the same
elements in the same percentages (ratios) - mixtures have variable composition
4Compounds Display Constant Composition
- If we decompose water by electrolysis, we find
16.0 grams of oxygen to every 2.00 grams of
hydrogen. - Water has a constant Mass Ratio of Oxygen to
Hydrogen of 8.0.
5Why do Compounds ShowConstant Composition
- smallest piece of a compound is called a molecule
- every molecule of a compound has the same number
and type of atoms as determined by the electronic
structures of the atoms (more on that later in
the year) - since all the molecules of a compound are
identical - every sample will have the same ratio of the
elements - every sample of the compound will have the same
properties
6EXAMPLE 5.1 Constant Composition of Compounds
Two samples of carbon dioxide, obtained from
different sources, were decomposed into their
constituent elements. One sample produced 4.8 g
of oxygen and 1.8 g of carbon, and the other
sample produced 17.1 g of oxygen and 6.4 g of
carbon. Show that these results are consistent
with the law of constant composition.
7What is the carbon-hydrogen mass ratio for
methane (CH4)?
5.3A
- 1
- 0.33
- 3
- 4
- 0.25
8If the mass ratio of lead(II) sulfide is 270.0 g
lead and 41.8 g sulfur, how much lead is required
to completely react with 85.6 g of sulfur?
5.1B
- 13.3
- 185
- 228
- 312
- 553
9Formulas Describe Compounds
water H2O \ two atoms of hydrogen and 1 atom of
oxygen table sugar C12H22O11 \12 atoms of C, 22
atoms of H and 11 atoms O
10Order of Elements in a Formula
- metals written first
- NaCl
- nonmetals written in order from Table 5.1
- CO2
- are occasional exceptions for historical or
informational reasons - H2O, but NaOH
Table 5.1
Order of Listing Nonmetals in Chemical Formulas C P N H S I Br Cl O F
11Molecules with Polyatomic Ions
Mg(NO3)2 compound called magnesium nitrate
CaSO4 compound called calcium sulfate
12Molecules with Polyatomic Ions
Mg(NO3)2 compound called magnesium nitrate
CaSO4 compound called calcium sulfate
13Classifying Materials
- atomic elements elements whose particles are
single atoms - molecular elements elements whose particles are
multi-atom molecules - molecular compounds compounds whose particles
are molecules made of only nonmetals - ionic compounds compounds whose particles are
cations and anions
14Molecular Elements
- Certain elements occur as 2 atom molecules
- Rule of 7s
- there are 7 common diatomic elements
- find the element with atomic number 7, N
- make a figure 7 by going over to Group 7A, then
down - dont forget to include H2
VIIA
7
H2
N2 O2 F2
Cl2
Br2
I2
15Molecular Compounds
- two or more nonmetals
- smallest unit is a molecule
16Ionic Compounds
- metals nonmetals
- no individual molecule units, instead have a
3-dimensional array of cations and anions made of
formula units
17Molecular View of Elements and Compounds
18Classify each of the following as either an
atomic element, molecular element, molecular
compound or ionic compound
- aluminum, Al
- aluminum chloride, AlCl3
- chlorine, Cl2
- acetone, C3H6O
- carbon monoxide, CO
- cobalt, Co
19Classify each of the following as either an
atomic element, molecular element, molecular
compound or ionic compound
- aluminum, Al atomic element
- aluminum chloride, AlCl3 ionic compound
- chlorine, Cl2 molecular element
- acetone, C3H6O molecular compound
- carbon monoxide, CO molecular compound
- cobalt, Co atomic element
20Formula-to-NameStep 1
- Is the compound one of the exceptions to the
rules?
- H2O water, steam, ice
- NH3 ammonia
21Formula-to-NameStep 2
- What major class of compound is it?
- Ionic or Molecular
22Major Classes
- Ionic
- metal nonmetal
- metal first in formula
- Binary Ionic
- compounds with polyatomic ions
- Molecular
- 2 nonmetals
- Binary Molecular (or Binary Covalent)
- Acids formula starts with H
- though acids are molecular, they behave as ionic
when dissolved in water - may be binary or oxyacid
23Formula-to-NameStep 3
- What major subclass of compound is it?
- Binary Ionic, Ionic with Polyatomic Ions,
- Binary Molecular,
- Binary Acid, Oxyacid
24Classifying Compounds
- Compounds containing a metal and a nonmetal
binary ionic - Type I and II
- Compounds containing a polyatomic ion ionic
with polyatomic ion - Compounds containing two nonmetals binary
molecular compounds - Compounds containing H and a nonmetal binary
acids - Compounds containing H and a polyatomic ion
oxyacids
25Formula-to-NameStep 4
- Apply Rules for the Class and Subclass
26Formula-to-NameRules for Ionic
- Made of cation and anion
- Name by simply naming the ions
- If cation is
- Type I metal metal name
- Type II metal metal name(charge)
- Polyatomic ion name of polyatomic ion
- If anion is
- Nonmetal stem of nonmetal name ide
- Polyatomic ion name of polyatomic ion
27Monatomic Nonmetal Anion
- determine the charge from position on the
Periodic Table - to name anion, change ending on the element name
to ide
4A -4 5A -3 6A -2 7A -1
C carbide N nitride O oxide F fluoride
Si silicide P phosphide S sulfide Cl chloride
28Metal Cations
- Type I
- metals whose ions can only have one possible
charge - IA, IIA, (Al, Ga, In)
- determine charge by position on the Periodic
Table - IA 1, IIA 2, (Al, Ga, In 3)
- Type II
- metals whose ions can have more than one possible
charge - determine charge by charge on anion
How do you know a metal cation is Type II?
its not Type I !!!
29Determine if the following metals are Type I or
Type II. If Type I, determine the charge on the
cation it forms.
- lithium, Li
- copper, Cu
- gallium, Ga
- tin, Sn
- strontium, Sr
30Determine if the following metals are Type I or
Type II. If Type I, determine the charge on the
cation it forms.
- lithium, Li Type I 1
- copper, Cu Type II
- gallium, Ga Type I 3
- tin, Sn Type II
- strontium, Sr Type I 2
31Type I Binary Ionic Compounds
- Contain Metal Cation Nonmetal Anion
- Metal listed first in formula name
- name metal cation first, name nonmetal anion
second - cation name is the metal name
- nonmetal anion named by changing the ending on
the nonmetal name to -ide
32Type II Binary Ionic Compounds
- Contain Metal Cation Nonmetal Anion
- Metal listed first in formula name
- name metal cation first, name nonmetal anion
second - metal cation name is the metal name followed by a
Roman Numeral in parentheses to indicate its
charge - determine charge from anion charge
- Common Type II cations in Table 5.5
- nonmetal anion named by changing the ending on
the nonmetal name to -ide
33Examples
- LiCl lithium chloride
- AlCl3 aluminum chloride
- PbO lead(II) oxide
- PbO2 lead(IV) oxide
- Mn2O3 manganese(III) oxide
- ZnCl2 zinc(II) chloride or zinc chloride
- AgCl silver(I) chloride or silver chloride
34Compounds Containing Polyatomic Ions
- Polyatomic ions are single ions that contain
more than one atom - Name any ionic compound by naming cation first
and then anion - Non-polyatomic cations named like Type I and II
- Non-polyatomic anions named with -ide
35Fixed Charge Metals and Nonmetals
IA
VIIA
VA
IIA
IIIA
VIA
Li1
Be2
O-2
F-1
N-3
Na1
Mg2
S-2
Cl-1
P-3
Al3
K1
Ca2
Se-2
Br-1
As-3
Ga3
Zn2
Rb1
Sr2
Te-2
I-1
In3
Cd2
Ag1
Cs1
Ba2
36Some Common Polyatomic Ions
Name Formula
acetate C2H3O2
carbonate CO32
hydrogen carbonate (aka bicarbonate) HCO3
hydroxide OH
nitrate NO3
nitrite NO2
chromate CrO42
dichromate Cr2O72
ammonium NH4
Name Formula
hypochlorite ClO
chlorite ClO2
chlorate ClO3
perchlorate ClO4
sulfate SO42
sulfite SO32
hydrogensulfate (aka bisulfate) HSO4
hydrogensulfite (aka bisulfite) HSO3
37Patterns for Polyatomic Ions
- elements in the same column form similar
polyatomic ions - same number of Os and same charge
- ClO3- chlorate \ BrO3- bromate
- if the polyatomic ion starts with H, the name
adds hydrogen- prefix before name and add 1 to
the charge - CO32- carbonate \ HCO3-1 hydrogencarbonate
38Periodic Pattern of Polyatomic Ions-ate groups
IIIA IVA VA VIA VIIA
39Binary Molecular Compounds of 2 Nonmetals
- Name first element in formula first
- use the full name of the element
- Name the second element in the formula with an
-ide - as if it were an anion, however, remember these
compounds do not contain ions! - Use a prefix in front of each name to indicate
the number of atoms - Never use the prefix mono- on the first element
40Subscript - Prefixes
- 1 mono - not used on first nonmetal
- 2 di-
- 3 tri-
- 4 tetra-
- 5 penta-
- 6 hexa-
- 7 hepta-
- 8 octa-
- 9 nona-
- 10 deca-
drop last a if name begins with vowel
41Acids
- Contain H1 cation and anion
- in aqueous solution
- Binary acids have H1 cation and nonmetal anion
- Oxyacids have H1 cation and polyatomic anion
42Formula-to-NameAcids
- acids are molecular compounds that often behave
like they are made of ions - All names have acid at end
- Binary Acids hydro prefix stem of the name of
the nonmetal ic suffix - Oxyacids
- if polyatomic ion ends in ate name of
polyatomic ion with ic suffix - if polyatomic ion ends in ite name of
polyatomic ion with ous suffix
43Example Naming Binary AcidsHCl
- Is it one of the common exceptions?
- H2O, NH3, CH4, NaCl, C12H22O11 No!
- Identify Major Class
- first element listed is H, ? Acid
- Identify the Subclass
- 2 elements, ? Binary Acid
44Sample - Naming Binary Acids HCl
- Identify the anion
- Cl Cl-, chloride because Group 7A
- Name the anion with an ic suffix
- Cl- chloride ? chloric
- Add a hydro- prefix to the anion name
- hydrochloric
- Add the word acid to the end
- hydrochloric acid
45Example Naming OxyacidsH2SO4
- Is it one of the common exceptions?
- H2O, NH3, CH4, NaCl, C12H22O11 No!
- Identify Major Class
- first element listed is H, ? Acid
- Identify the Subclass
- 3 elements in the formula, ? Oxyacid
46Example Naming Oxyacids H2SO4
- Identify the anion
- SO4 SO42- sulfate
- If the anion has ate suffix, change it to ic.
If the anion has ite suffix, change it to -ous - SO42- sulfate ? sulfuric
- Write the name of the anion followed by the word
acid - sulfuric acid
- (kind of an exception, to make it sound nicer!)
47Example Naming Oxyacids H2SO3
- Is it one of the common exceptions?
- H2O, NH3, CH4, NaCl, C12H22O11 No!
- Identify Major Class
- first element listed is H, ? Acid
- Identify the Subclass
- 3 elements in the formula, ? Oxyacid
48Example Naming Oxyacids H2SO3
- Identify the anion
- SO3 SO32- sulfite
- If the anion has ate suffix, change it to ic.
If the anion has ite suffix, change it to -ous - SO32- sulfite ? sulfurous
- Write the name of the anion followed by the word
acid - sulfurous acid
49 Formula-to-Name Flow Chart
50Name to Formula
51Writing the Formulas from the Names
- For binary molecular compounds, use the prefixes
to determine the subscripts - For Type I, Type II, Ternary Compounds and Acids
- Determine the ions present
- Determine the charges on the cation and anion
- Balance the charges to get the subscripts
52Example Binary Moleculardinitrogen pentoxide
- Identify the symbols of the elements
- nitrogen N
- oxide oxygen O
- Write the formula using prefix number for
subscript - di 2, penta 5
- N2O5
53Compounds that Contain Ions
- compounds of metals with nonmetals are made of
ions - metal atoms form cations, nonmetal atoms for
anions - compound must have no total charge, therefore we
must balance the numbers of cations and anions in
a compound to get 0 charge - if Na is combined with S2-, you will need 2 Na
ions for every S2- ion to balance the charges,
therefore the formula must be Na2S
54Writing Formulas for Ionic Compounds
- Write the symbol for the metal cation and its
charge - Write the symbol for the nonmetal anion and its
charge - Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the sum of the charges of the cation
cancels the sum of the anions
55Write the formula of a compound made from
aluminum ions and oxide ions
- Write the symbol for the metal cation and its
charge - Write the symbol for the nonmetal anion and its
charge - Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the total charge of the cations
cancels the total charge of the anions
Al3 column IIIA
O2- column VIA
Al3 O2-
Al2 O3
Al (2)(3) 6 O (3)(-2) -6
56Practice - What are the formulas for compounds
made from the following ions?
- potassium ion with a nitride ion
- calcium ion with a bromide ion
- aluminum ion with a sulfide ion
57Practice - What are the formulas for compounds
made from the following ions?
- K with N3- K3N
- Ca2 with Br- CaBr2
- Al3 with S2- Al2S3
58Example Ionic Compoundsmanganese(IV) sulfide
- Write the symbol for the cation and its charge
- Write the symbol for the anion and its charge
- Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the total charge of the cations
cancels the total charge of the anions
Mn4
S2-
Mn4 S2-
Mn2S4
MnS2
Mn (1)(4) 4 S (2)(-2) -4
59Example Ionic CompoundsIron(III) phosphate
- Write the symbol for the cation and its charge
- Write the symbol for the anion and its charge
- Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the total charge of the cations
cancels the total charge of the anions
Fe3
PO43-
Fe3 PO43-
Fe3(PO4)3
FePO4
Fe (1)(3) 3 PO4 (1)(-3) -3
60Example Ionic Compoundsammonium carbonate
- Write the symbol for the cation and its charge
- Write the symbol for the anion and its charge
- Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the total charge of the cations
cancels the total charge of the anions
NH4
CO32-
NH4 CO32-
(NH4)2CO3
(NH4)2CO3
NH4 (2)(1) 2 CO3 (1)(-2) -2
61Practice - What are the formulas for compounds
made from the following ions?
- copper(II) ion with a nitride ion
- iron(III) ion with a bromide ion
- aluminum ion with a sulfate ion
62Practice - What are the formulas for compounds
made from the following ions?
- Cu2 with N3- Cu3N2
- Fe3 with Br- FeBr3
- Al3 with SO42- Al2(SO4)3
63Example Binary Acidshydrosulfuric acid
in all acids the cation is H
- Write the symbol for the cation and its charge
- Write the symbol for the anion and its charge
- Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the total charge of the cations
cancels the total charge of the anions
H
hydro means binary
S2-
H S2-
H2S
H2S
H (2)(1) 2 S (1)(-2) -2
64Example Oxyacidscarbonic acid
in all acids the cation is H
- Write the symbol for the cation and its charge
- Write the symbol for the anion and its charge
- Charge (without sign) becomes subscript for other
ion - Reduce subscripts to smallest whole number ratio
- Check that the total charge of the cations
cancels the total charge of the anions
H
no hydro means polyatomic ion
CO32-
-ic means -ate ion
H CO32-
H2CO3
H2CO3
H (2)(1) 2 CO3 (1)(-2) -2
65Practice - What are the formulas for the
following acids?
- chlorous acid
- phosphoric acid
- hydrobromic acid
66Practice - What are the formulas for the
following acids?
- H with ClO2 HClO2
- H with PO43 H3PO4
- H with Br HBr
67Formula Mass
- the mass of an individual molecule or formula
unit - also known as molecular mass or molecular weight
- sum of the masses of the atoms in a single
molecule or formula unit - whole sum of the parts!
- mass of 1 molecule of H2O
- 2(1.01 amu H) 16.00 amu O 18.02 amu
68EXAMPLE 5.1 Constant Composition of Compounds
Two samples of carbon dioxide, obtained from
different sources, were decomposed into their
constituent elements. One sample produced 4.8 g
of oxygen and 1.8 g of carbon, and the other
sample produced 17.1 g of oxygen and 6.4 g of
carbon. Show that these results are consistent
with the law of constant composition.
69EXAMPLE 5.2 Writing Chemical Formulas
Write a chemical formula for each of the
following (a) the compound containing two
aluminum atoms to every three oxygen atoms (b)
the compound containing three oxygen atoms to
every sulfur atom (c) the compound containing
four chlorine atoms to every carbon atom
70EXAMPLE 5.3 Total Number of Each Type of Atom
in a Chemical Formula
Determine the number of each type of atom in
Mg3(PO4)2.
SolutionMg There are three Mg atoms, as
indicated by the subscript 3. P There are two
P atoms, as we see by multiplying the subscript
outside the parentheses (2) by the subscript for
P inside the parentheses, which is 1
(implied). O There are eight O atoms, as we see
by multiplying the subscript outside the
parentheses (2) by the subscript for O inside
the parentheses (4).
71EXAMPLE 5.4 Classifying Substances as Atomic
Elements, Molecular Elements, Molecular
Compounds, or Ionic Compounds
Classify each of the following substances as an
atomic element, molecular element, molecular
compound, or ionic compound. (a) krypton (b)
CoCl2 (c) nitrogen (d) SO2 (e) KNO3
Solution(a) Krypton is an element that is not
listed as diatomic in Table 5.2 therefore, it is
an atomic element. (b) CoCl2 is a compound
composed of a metal (left side of periodic table)
and nonmetal (right side of the periodic
table) therefore, it is an ionic compound. (c)
Nitrogen is an element that is listed as diatomic
in Table 5.2 therefore, it is a molecular
element. (d) SO2 is a compound composed of two
nonmetals therefore, it is a molecular
compound. (e) KNO3 is a compound composed of a
metal and two nonmetals therefore, it is an
ionic compound.
72EXAMPLE 5.5 Writing Formulas for Ionic Compounds
Write a formula for the ionic compound that forms
from aluminum and oxygen.
73EXAMPLE 5.6 Writing Formulas for Ionic Compounds
Write a formula for the ionic compound that forms
from magnesium and oxygen.
74EXAMPLE 5.7 Writing Formulas for Ionic Compounds
Write a formula for the compound that forms from
potassium and oxygen.
SolutionWe first write the symbol for each ion
along with its appropriate charge from its group
number in the periodic table. K O2 We then
make the magnitude of each ions charge become
the subscript for the other ion. K O2
becomes K2O No reducing of subscripts is
necessary in this case. Finally, we check to see
that the sum of the charges of the cations 2(1)
2 exactly cancels the sum of the charges of
the anion (2). The correct formula is K2O.
75EXAMPLE 5.8 Naming Type I Ionic Compounds
Give the name for the compound MgF2.
SolutionThe cation is magnesium. The anion is
fluorine, which becomes fluoride. The correct
name is magnesium fluoride.
76EXAMPLE 5.9 Naming Type II Ionic Compounds
Give the name for the compound PbCl4.
SolutionThe name for PbCl4 consists of the name
of the cation, lead, followed by the charge of
the cation in parenthesis (IV), followed by the
base name of the anion, chlor-, with the ending
-ide. The full name is lead(IV) chloride. We know
the charge on Pb is 4 because the charge on Cl
is 1. Since there are 4 Cl anions, the Pb
cation must be Pb4. PbCl4 lead (IV) chloride
77EXAMPLE 5.10 Naming Ionic Compounds That
Contain a Polyatomic Ion
Give the name for the compound K2CrO4.
78EXAMPLE 5.11 Naming Molecular Compounds
Name each of the following CCl4 BCl3
SF6.
Solution CCl4 The name of the compound is
the name of the first element, carbon, followed
by the base name of the second element, chlor,
prefixed by tetra- to indicate four, and the
suffix -ide. The entire name is carbon
tetrachloride. BCl3 The name of the compound
is the name of the first element, boron, followed
by the base name of the second element, chlor,
prefixed by tri- to indicate three, and the
suffix -ide. The entire name is boron
trichloride. SF4 The name of the compound
is the name of the first element, sulfur,
followed by the base name of the second element,
fluor, prefixed by hexa- to indicate six, and the
suffix -ide. The entire name is sulfur
hexafluoride.
79EXAMPLE 5.12 Naming Binary Acids
Give the name of H2S.
80EXAMPLE 5.13 Naming Oxyacids
Give the name of HC2H3O2.
81EXAMPLE 5.14 Nomenclature Using Figure 5.17
Name each of the following CO, CaF2, HF,
Fe(NO3)3, HClO4, H2SO3
82EXAMPLE 5.15 Calculating Formula Mass
Calculate the formula mass of carbon
tetrachloride, CCl4.
Solution To find the formula mass, we sum the
atomic masses of each atom in the chemical
formula. Formula mass 1 x (Formula mass C)
4 x (Formula mass Cl) 12.01 amu 4(35.45
amu) 153.81 amu
83EXAMPLE 5.16 Constant Composition of Compounds
Two samples said to be carbon disulfide (CS2) are
decomposed into their constituent elements. One
sample produced 8.08 g S and 1.51 g C, while the
other produced 31.3 g S and 3.85 g C. Are these
results consistent with the law of constant
composition?
84EXAMPLE 5.17 Writing Chemical Formulas
Write a chemical formula for the compound
containing one nitrogen atom for every two oxygen
atoms.
Solution NO2
85EXAMPLE 5.18 Total Number of Each Type of Atom
in a Chemical Formula
Determine the number of each type of atom in
PB(ClO3)2.
Solution One Pb atom Two Cl atoms Six O atoms
86EXAMPLE 5.19 Classifying Elements as Atomic or
Molecular
Classify each of the following elements as atomic
or molecular Na, I, N.
Solution Na atomic I molecular (I2) N
molecular (N2)
87EXAMPLE 5.20 Classifying Compounds as Ionic or
Molecular
Classify each of the following compounds as ionic
or molecular. If they are ionic, classify them as
Type I or Type II ionic compounds FeCl3,
K2SO4, CCl4
Solution FeCl3 ionic, Type II K2SO4
ionic, Type I CCl4 molecular
88EXAMPLE 5.21 Writing Formulas for Ionic
Compounds
Write a formula for the compound that forms from
lithium and sulfate ions.
89EXAMPLE 5.22 Naming Type I Binary Ionic
Compounds
Give the name for the compound Al2O3
Solution aluminum oxide
90EXAMPLE 5.23 Naming Type II Binary Ionic
Compounds
Give the name for the compound Fe2S3
Solution 3 sulfide ions x (2) 6 2 iron
ions x (?) 6 ? 3 Charge of each
iron ion 3 iron(III) sulfide
91EXAMPLE 5.24 Naming Compounds Containing a
Polyatomic Ion
Give the name for the compound Co(ClO4)2.
Solution 3 perchlorate x (1) 2 Charge
of cobalt ion 2 cobalt(II) perchlorate
92EXAMPLE 5.25 Naming Molecular Compounds
Name the compound NO2.
Solution nitrogen dioxide
93EXAMPLE 5.26 Naming Binary Acids
Name the acid HI.
Solution hydroiodic acid
94EXAMPLE 5.27 Naming Oxyacids with an Oxyanion
Ending in -ate
Name the acid H2SO4.
Solution The oxyanion is sulfate. The name of
the acid is sulfuric acid.
95EXAMPLE 5.28 Naming Oxyacids with an Oxyanion
Ending in -ite
Name the acid HClO2.
Solution The oxyanion is chlorite. The name of
the acid is chlorous acid.
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100EXAMPLE 5.29 Calculating Formula Mass
Calculate the formula mass of Mg(NO3)2
Solution Formula mass 24.31 2(14.01)
6(16.00) 148.33 amu