Introductory Chemistry, 2nd Edition Nivaldo Tro

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Introductory Chemistry, 2nd EditionNivaldo Tro
Chapter 5 Molecules and Compounds
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Molecules and Compounds

• Compounds composed of 2 or more elements
  chemically combined
• Properties completely different from component
  elements
• Salt
• Sodium (Na) shiny, reactive, poisonous
• Chlorine (Cl) pale yellow gas, reactive,
  poisonous
• Sodium chloride (NaCl) table salt, flavor
  enhancer

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Law of Constant Composition

• Pure substances have constant composition
• all samples of a pure substance contain same
  elements in same ratios or proportions regardless
  of source
• mixtures have variable composition

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Compounds Display Constant Composition

• Water (H2O) decomposed by electrolysis yields
  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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Formulas Describe Compounds

• Compound a distinct substance that is composed
  of atoms of two or more elements
• Formulas give the number and type of each atom in
  the simplest unit of the compound
• Molecules (H2O) or ions (CaCl2)
• Number of atoms of each element is written to the
  right of the element as a subscript
• if only one atom, 1 subscript is not written
• Polyatomic groups are placed in parentheses
• if more than one, i. e. Ca(NO3)2

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Formulas Describe Compounds
Examples water H2O \ two atoms of hydrogen and
1 atom of oxygen table sugar (sucrose)
C12H22O11 \12 atoms of C, 22 atoms of H and 11
atoms O
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Classifying Materials

• Atomic elements elements whose particles are
  single atoms Na, Ne, Hg, Ag
• Molecular elements elements whose particles are
  multi-atom molecules H2, O2, N2, Cl2

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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

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Classifying Materials

• Molecular compounds compounds whose particles
  are molecules made of only nonmetals, i.e. CO2
• Ionic compounds compounds whose particles are
  cations () and anions (-), i.e. NaCl

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Molecular Compounds

• Two or more nonmetals, i.e. H2O, CO2, C6H12O6
• Smallest unit is a molecule

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Order of Elements in a Formula

• Metals written first
• NaCl
• Nonmetals written in order from Table 5.1
• CO2
• occasional exceptions for historical or
  informational reasons
• H2O, but NaOH

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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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Major Classes of Compounds

• 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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Binary Ionic CompoundsWriting a correct formula

• 1. Write down the charges of the stable ions with
  the positive ion first.

Ex for Chlorine and magnesium Mg Cl
1-
2
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2. Cross-over charges to get subscripts. Drop
all /- signs.
Ex for Chlorine and magnesium Mg Cl
1 -
2
1
2
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3. Reduce/Simplify subscripts to get the lowest
whole number ratio. The subscript 1 does not
have to be shown.
Ex for Chlorine and magnesium MgCl2
Ex calcium and sulfur Ca2S-2
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How many electrons will an atom lose or gain in
an ionic compound?
lose 1 e-
gain 3 e-
gain 2 e-
gain 1 e-
lose 2 e-
lose 3 e-
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What will be the charge on the stable ion
formed?
1
2
3
-3
-2
-1
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Rules for Naming Ionic Compounds from Formula

• Made of cation and anion
• Name by simply naming the ions
• If cation is
• Type I metal (main group) metal name
• Type II metal (transition element) metal
  name(charge)
• Polyatomic ion name of polyatomic ion
• If anion is
• Nonmetal root of nonmetal name ide
• Polyatomic ion name of polyatomic ion

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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 (transition elements)
• 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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Determining Charge and Naming Monatomic Nonmetal
Anions

• 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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Naming 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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What is the correct formula and name for a
compound made from

• 1. nitrogen and potassium
• 2. magnesium and oxygen
• 3. chlorine and calcium
• 4. oxygen and aluminum

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1. nitrogen and potassium K3N potassium
nitride 2. magnesium and oxygen MgO magnesium
oxide 3. chlorine and calcium CaCl2 calcium
chloride 4. oxygen and aluminum Al2O3 aluminum
oxide
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Naming Type II Binary Ionic Compounds

• 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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Example Naming Binary Ionic, Type II MetalCuCl

• Identify Major Class
• Cu metal, on left side of Periodic Table
• Cl nonmetal, on right side of Periodic Table
• ? Ionic
• Identify the Subclass 2 elements,
• ? Binary Ionic
• Is the metal Type I or Type II
• Cu not in Group IA, IIA, or (Al, Ga, In) ? Type II

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Example Naming Binary Ionic, Type II Metal CuCl

• Identify cation and anion
• Cl Cl- because it is Group 7
• Cu Cu to balance the charge
• Name the cation
• Cu copper(I)
• Name the anion
• Cl- chloride
• Write the cation name first, then the anion name
• copper(I) chloride

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Give the formula and name for a compound from
Cu1 and sulfur
name copper(I) sulfide
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Give the formula and name for a compound from
Fe2 and chlorine
Give the formula and name for a compound from
Cu2 and sulfur
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What is the formula for copper(II) oxide?
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Compounds with Polyatomic Ions

• Polyatomic ions are single ions that contain more
  than one atom
• Formula cation first, polyatomic anion or
  polyatomic cation, monatomic anion
• Name cation first and then anion
• Non-polyatomic cations named like Type I and II
• Non-polyatomic anions named with ide
• Polyatomic ions use name of polyatomic ion

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Some Common Polyatomic Ions(be able to recognize
these)
Name Formula and Charge
acetate C2H3O2
carbonate CO32
hydrogen carbonate (aka bicarbonate) HCO3
hydroxide OH
nitrate NO3
nitrite NO2
sulfate SO42
chlorate ClO3
ammonium NH4
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Naming Ionic Compounds with Polyatomic Ion
Na2SO4

• Identify Major Class
• Na metal, on the left side of Periodic Table
• SO4 is a polyatomic ion, ? Ionic
• Identify the Subclass
• compound has 3 elements ? Ionic with Polyatomic
  Ion
• Is the metal Type I or Type II
• Na is in Group IA, ? Type I

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Naming Ionic Compounds with Polyatomic Ion
Na2SO4

• Identify the ions
• Na Na because in Group 1
• SO4 SO42- a polyatomic ion
• Name the cation
• Na sodium (Type I)
• Name the anion
• SO42- sulfate
• Write the name of the cation followed by the name
  of the anion
• sodium sulfate

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Naming Ionic Compounds with Polyatomic Ion
Fe(NO3)3

• Identify Major Class
• Fe metal, on left side of Periodic Table
• NO3 is a polyatomic ion because it is in ( )
• ? Ionic
• Identify the Subclass
• Have 3 elements ? Ionic with Polyatomic Ion
• Is the metal Type I or Type II
• Fe not in Group IA, IIA, or (Al, Ga, In) ? Type II

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Naming Ionic compounds with Polyatomic Ion
Fe(NO3)3

• Identify the ions
• NO3 NO3- a polyatomic ion
• Fe Fe3 to balance the charge of the 3 NO3-1
• Name the cation
• Fe3 iron(III) (Type II)
• Name the anion
• NO3- nitrate
• Write the name of the cation followed by the name
  of the anion
• iron(III) nitrate

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Rules for Naming Binary Molecular Compounds

• Binary molecular compounds composed of 2
  nonmetal elements
• for binary molecular compound
• name first nonmetal
• then name second nonmetal with ide ending
• then give each name a prefix to indicate number
  of atoms (subscript) of each element in formula

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Naming Binary Molecular Compounds

• 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-
• drop last a if name begins with vowel

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Naming Binary Molecular Compounds BF3

• Identify Major Class
• B nonmetal, on right side of Periodic Table
• F nonmetal, on right side of Periodic Table
• ? Molecular
• Identify the Subclass
• 2 elements ? Binary Molecular

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Naming Binary Molecular Compounds BF3

• Name the first element boron
• Name the second element with an ide
• fluorine ? fluoride
• Add a prefix to each name to indicate the
  subscript
• monoboron, trifluoride
• Write the first element with prefix, then the
  second element with prefix
• Drop prefix mono from first element
• boron trifluoride

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Formula Mass

• Formula mass 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