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
• 0.33
• 3
• 4
• 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

• 13.3
• 185
• 228
• 312
• 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

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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

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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
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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

• 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

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Write 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
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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

• 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
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Example 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
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Example 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
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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

• 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
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Example 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
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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