Chapter 5 Molecules and Compounds

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Chapter 5Molecules andCompounds
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Molecules 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

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Law 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
• 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.

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Why 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

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Example Constant Composition
EXAMPLE 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.
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Examples Using Mass Ratios
What is the carbon-hydrogen mass ratio for
methane (CH4)?
5.3A

1. 1
2. 0.33
3. 3
4. 4
5. 0.25

If 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

1. 13.3
2. 185
3. 228
4. 312
5. 553

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Formulas 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
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Order 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
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Molecules with Polyatomic Ions
Mg(NO3)2 compound called magnesium nitrate
CaSO4 compound called calcium sulfate
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Molecules with Polyatomic Ions
Mg(NO3)2 compound called magnesium nitrate
CaSO4 compound called calcium sulfate
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Classifying 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

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Molecular 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
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Molecular Compounds

• two or more nonmetals
• smallest unit is a molecule

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Ionic Compounds

• metals nonmetals
• no individual molecule units, instead have a
  3-dimensional array of cations and anions made of
  formula units

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Molecular View of Elements and Compounds
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Classify 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

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Classify 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

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Formula-to-NameStep 1

• Is the compound one of the exceptions to the
  rules?

• H2O water, steam, ice
• NH3 ammonia

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Formula-to-NameStep 2

• What major class of compound is it?
• Ionic or Molecular

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Major 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

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Formula-to-NameStep 3

• What major subclass of compound is it?
• Binary Ionic, Ionic with Polyatomic Ions,
• Binary Molecular,
• Binary Acid, Oxyacid

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Classifying 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

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Formula-to-NameStep 4

• Apply Rules for the Class and Subclass

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Formula-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

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Monatomic 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
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Metal 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 !!!
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Determine 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

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Determine 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

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Type 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

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Type 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

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Examples

• 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

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Compounds 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

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Fixed 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
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Some 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
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Patterns 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

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Periodic Pattern of Polyatomic Ions-ate groups
IIIA IVA VA VIA VIIA
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Binary 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

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Subscript - 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
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Acids

• Contain H1 cation and anion
• in aqueous solution
• Binary acids have H1 cation and nonmetal anion
• Oxyacids have H1 cation and polyatomic anion

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Formula-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

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Example 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

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Sample - 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

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Example 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

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Example 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!)

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Example 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

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Example 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

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Formula-to-Name Flow Chart
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Name to Formula
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Writing 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

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Example 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

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Compounds 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

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Writing Formulas for Ionic Compounds

1. Write the symbol for the metal cation and its
   charge
2. Write the symbol for the nonmetal anion and its
   charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. Check that the sum of the charges of the cation
   cancels the sum of the anions

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Write the formula of a compound made from
aluminum ions and oxide ions

1. Write the symbol for the metal cation and its
   charge
2. Write the symbol for the nonmetal anion and its
   charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. 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
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Practice - 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

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Practice - What are the formulas for compounds
made from the following ions?

• K with N3- K3N
• Ca2 with Br- CaBr2
• Al3 with S2- Al2S3

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Example Ionic Compoundsmanganese(IV) sulfide

1. Write the symbol for the cation and its charge
2. Write the symbol for the anion and its charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. 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
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Example Ionic CompoundsIron(III) phosphate

1. Write the symbol for the cation and its charge
2. Write the symbol for the anion and its charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. 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
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Example Ionic Compoundsammonium carbonate

1. Write the symbol for the cation and its charge
2. Write the symbol for the anion and its charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. 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
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Practice - 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

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Practice - 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

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Example Binary Acidshydrosulfuric acid
in all acids the cation is H

1. Write the symbol for the cation and its charge
2. Write the symbol for the anion and its charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. 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
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Example Oxyacidscarbonic acid
in all acids the cation is H

1. Write the symbol for the cation and its charge
2. Write the symbol for the anion and its charge
3. Charge (without sign) becomes subscript for other
   ion
4. Reduce subscripts to smallest whole number ratio
5. 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
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Practice - What are the formulas for the
following acids?

• chlorous acid
• phosphoric acid
• hydrobromic acid

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Practice - What are the formulas for the
following acids?

• H with ClO2 HClO2
• H with PO43 H3PO4
• H with Br HBr

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Formula 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