4.1 Representing Ionic Compounds

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4.1 Representing Ionic Compounds
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Forming Ionic Compounds

• Ionic compounds are formed when one or more
  valence electrons (electrons in the outer energy
  level) are transferred from a metal atom to a
  non-metal atom.
• Example sodium chloride (NaCl)
• they are made up of positive ions (cations) and
  negative ions (anions) that are attracted to each
  other.
• the two oppositely charged ions are attracted to
  each other by a force called an ionic bond.

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The Periodic Table and Valence Electrons
Group 8 8 valence electrons
Except for He, it has 2 electrons
Group 1 1 valence electron
Group 2 2 valence electrons

• Each column is called a group

• Octet Rule The loss and gain of electrons allows
  each atom to form a full outer energy level of
  electrons and, therefore, become stable (with the
  same number of electrons as the closest noble
  gas)
• Scientists often refer to this arrangement as a
  stable octet.

13, 14, 15, 16, 17
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Ionic structure / properties

• Ionic compounds are solids at SATP. In their
  solid form they form ionic crystals. These are
  more commonly known as salts.
• high melting and boiling points
• many are brittle
• when ionic compounds are dissolved in water, they
  dissociate into their ions and the solutions
  conduct electricity.
• NaCl(s) ? Na(aq) Cl-(aq)

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Types of Ionic Compounds

• Binary Ionic Compounds composed of only 2
  different elements (a metal cation and a
  non-metal anion)
• some binary ionic compounds contain a multivalent
  metal these have more than one ion charge
  (listed in the periodic table)
• Ternary Ionic Compound composed of 3 different
  elements (one of the ions is polyatomic made up
  of more than one element)

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Naming Binary Ionic Compounds
Binary Ionic Compounds

• The metal ion is always written first and keeps
  its whole name
• The non-metal is written second and has a slight
  change, the ending (suffix) is changed to ide
• -example Na2S sodium sulfide

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Writing Formulas for Binary Ionic Compounds
Binary Ionic Compounds

• -example magnesium chloride
• Step 1 Write the symbols with the metal first
• Mg Cl
• Step 2 Write the ionic charge above each symbol
  to indicate the stable
• ion that each element forms
• 2 1-
• Mg Cl
• Step 3 Determine how many ions of each type you
  need so that the total
• ionic charge is zero
• One Mg2 ion will balance the charge of two Cl-
  ions
• (2) 2(1-) 0
• Step 4 Write the formula using subscripts to
  indicate the number of ions
• of each type MgCl2

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Writing Formulas for Binary Ionic Compounds

• -example lithium oxide
• Step 1 Write the symbols with the metal first
• Li O
• Step 2 Write the ionic charge above each symbol
  to indicate the stable
• ion that each element forms
• 1 2-
• Li O
• Step 3 Determine how many ions of each type you
  need so that the total
• ionic charge is zero
• Two Li1 ions will balance the charge of one O-
  ion
• 2(1) (2-) 0
• Step 4 Write the formula using subscripts to
  indicate the number of ions
• of each type Li2O

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The Cross-Over Method

• -example lithium oxide
• Step 1 Write the symbols with the metal first
• Li O
• Step 2 Cross-Over Rule Write the ionic charge
  above each symbol and
• cross over the amount of charge.
• 1 2-
• Li O
• The formula is Li2O

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The Cross-Over Method

• -example calcium oxide
• Step 1 Write the symbols with the metal first
• Ca O
• Step 2 Cross-Over Rule Write the ionic charge
  above each symbol and
• cross over the amount of charge
• 2 2-
• Ca O
• The formula is Ca2O2
• Step 3 Reduce the Chemical Formula - Dividing by
  common factor of 2, we get
• CaO

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The Zero-Sum Rule
The sum of all the charges in the chemical
formula of the compound MUST EQUAL ZERO.
Example Al2S3
Ratio of 2 Al atoms 3 S atoms
Al cation ? 3 charge S anion ? -2 charge
2(3) 3(-2) ZERO! Al S
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Naming Binary Ionic Compounds having Multivalent
Metals
Binary Ionic Compounds

• -example FeS
• Step 1 Identify the metal
• Iron (Fe)
• Step 2 Verify that the metal can form more than
  one kind of ion by checking the periodic table.
• 2 3
• Fe and Fe
• Step 3 Determine the ratio of the ions in the
  chemical formula
• 1 iron 1 sulfide
• Step 4 Note the charge of the anion 2-

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• -example FeS
• Step 5 The positive and negative charges must
  balance out so that the net charge is 0.
• Total negative charge 2-
• Total positive charge 2
• Step 6 Determine what charge the metal ion must
  have to balance the anion.
• 1(Fe ?) 2
• Therefore, the charge on the iron must be 2.
• Step 7 Write the name of the metal ion include
  a roman numeral to show which charge the ion has
  in brackets, after the name. See Table 4.5 on pg.
  147.
• The name of the metal ion is iron(II)
• Step 8 Write the name of the compound.
• iron(II) sulfide

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Naming Ionic Compounds having Multivalent Metals
Binary Ionic Compounds

• -example Fe2S3
• Step 1 Identify the Metal
• Iron (Fe)
• Step 2 Verify that the metal can form more than
  one kind of ion by checking the periodic table
• 2 3
• Fe and Fe
• Step 3 Determine the ratio of the ions in the
  chemical formula
• 2 iron 3 sulfide
• Step 4 Note the charge of the anion 2-

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• -example Fe2S3
• Step 5 The positive and negative charges must
  balance out so that the net charge is 0.
• Total negative charge 6- (3 X 2-)
• Total positive charge 6
• Step 6 Determine what charge the metal ion must
  have to balance the anion.
• 2(Fe ?) 6
• Therefore, the charge on the iron must be 3.
• Step 7 Write the name of the metal ion include
  a roman numeral to show which charge the ion has
  in brackets after the name.
• The name of the metal ion is
  iron(III)
• Step 8 Write the name of the compound.
• iron(III) sulfide

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Writing Formulas for Binary Ionic Compounds
having Multivalent Metals
Binary Ionic Compounds

• -example tin(IV) sulfide
• Step 1 Write the symbols with the metal first
• Sn S
• Step 2 Cross-Over Rule Write the ionic charge
  above each symbol and
• cross over the amount of charge
• 4 2-
• Sn S
• The formula is Sn2S4
• Step 3 Reduce the Chemical Formula - Dividing by
  common factor of 2, we get
• SnS2

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Ternary Ionic CompoundsIonic Compounds with
Polyatomic Ions

• naming compounds with polyatomic ions is similar
  to naming other ionic compounds
• You should note that compounds with polyatomic
  ions have names ending in -ate or ite, not -ide
• Note that most are negative, except ammonium, NH4
  (see table 4.7 on pg. 148)
• Name Ca(OH)2, CuSO4, NH4NO3, Co2(CO3)3

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Answers
Ionic Compounds with Polyatomic Ions
- calcium hydroxide - copper(II) sulfate -
ammonium nitrate - cobalt(III) carbonate
Ca(OH)2 CuSO4 NH4NO3 Co2(CO3)3
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Most Common Polyatomic Ions
One extra oxygen "per-____-ate" Common/Normal Just memorize this one and youll know the rest One less oxygen -ite" Two less oxygens "hypo-____-ite"
NO41- pernitrate NO31- nitrate NO21- nitrite NO1- hyponitrite
CO42- percarbonate CO32- carbonate CO22- carbonite CO2- hypocarbonite
ClO41- perchlorate ClO31- chlorate ClO21- chlorite ClO1- hypochlorite
SO52- persulfate SO42- sulfate SO32- sulfite SO22- hyposulfite
PO53- perphosphate PO43- phosphate PO33- phosphite PO23- hypophosphite
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Writing Formulas
Ionic Compounds with Polyatomic ions

• -example aluminum carbonate
• Step 1 Using the periodic table and a table of
  common polyatomic ions, identify each ion and its
  charge.
• Aluminum Al3
• Carbonate CO32-
• Step 2 Cross-Over Rule Cross over the amount
  of charge.
• 3 2-
• Al CO3
• Step 3 Use subscripts to show the ratio of ions.
  Place the polyatomic ion in brackets, if it needs
  a subscript.
• Al2(CO3)3

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Writing Formulas
Ionic Compounds with Polyatomic ions

• -example ammonium sulfate
• Step 1 Using the periodic table and a table of
  common polyatomic ions, identify each ion and its
  charge.
• Ammonium NH4
• Sulfate SO4 2-
• Step 2 Cross-Over Rule Cross over the amount
  of charge.
• 1 2-
• NH4 SO4
• Step 3 Use subscripts to show the ratio of ions.
  Place the polyatomic ion in brackets, if it needs
  a subscript.
• (NH4)2SO4