Chemical Formulas and Compounds

1
Chapter 7

• Chemical Formulas and Compounds
• Date Started March 25, 2009

KCl
CaS
FeO
CuBr
2
Chemical formula and compounds

• Chemical formula show the types of atoms and
  their ratios to each other in a chemical
  compound.
• The subscripts show numerically the ratio of each
  atom in the compound and are always whole
  numbers.
• When the ratios of the compounds are simple whole
  number ratios, the formula is called an empirical
  formula.
• When polyatomic ions are in a chemical formula
  sometimes parentheses are needed within the
  formula.

C8H18 8 carbon atoms 18 hydrogen atoms
Al2(SO4)3 2 aluminum ions 3 sulfate ions
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Monatomic Ions

• Ions formed from a single atom are called
  monatomic ions.
• Some main groups elements do not form ions,
  rather they share their valence electrons.
  Carbon and silicon are examples of these types.
• Elements in group 14 can easily lose their
  s-orbital electrons, but do not readily give
  up their p-orbital electrons.
• Elements in the d-block tend to lose their
  electrons and have charges of 1, 2, 3, and 4.
  They are called polyvalent ions.
• For this reason, ion for the d-block elements
  must be looked up to find their common ion
  charges.
• The term oxidation number is sometimes used to
  refer to the apparent charge of an ion. (Very
  common with elements in groups 3-12)

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Naming Monatomic ions

• Negative monatomic ions change the endings of
  their name to ide.
• Positive ions are simply named by their element
  name, however when a atom has more than one
  positive charge state(polyvalent), roman numerals
  are used to indicate the charge.
• Page 221, Table 7-1, has some of the common
  monatomic ions and their charges.

K1 potassium ion Al3
Aluminum ion Fe2 iron(II) ion Fe3
iron(III) ion
F-1 fluoride ion S-2 sulfide ion N-3
nitride ion
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Common Ions and their Oxidation Numbers
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Binary ionic compounds

• Binary compounds are compounds composed of two
  different elements.
• The net (overall) charge in a binary compound
  must be equal to zero. This means all of the
  positive charges equals the negative charges.
• Subscripts are used to balance ions with
  different ionic charges.
• The cation is always written first followed by
  the anion.
• In naming binary compounds, the use of the
  monatomic ion names are the basis for naming the
  compound.

MgBr2 magnesium bromide
K2S potassium sulfide
FeO iron(II) oxide Fe2O3 iron(III)
oxide
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Balancing binary compounds

• Write the symbols for the ions with the cation
  first.
• Cross over charges to give the subscripts.
• Make sure that subscripts are simple whole number
  ratios. If they are not, reduce them by dividing
  by their largest common factor.
• Never indicate the cross over charge in the
  subscript.

• magnesium and chlorine
• Mg2 Cl-1
• Cross over Mg2Cl-1
  1 2
• Remove superscripts MgCl2
• The name of the compound is magnesium chloride.

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Stock system of nomenclature

• When ions have more than one possible positive
  charge, in writing the name of the compound,
  roman numerals are used to show the charge.
• If there is only one possible positive charge for
  a cation, roman numerals are NEVER used.
• Iron(II) is an ion with an iron atom having a
  charge of Fe2.
• Iron(III) is an ion with an iron atom having a
  charge of Fe3.

FeCl2 Iron(II) chloride
FeCl3 Iron(III) chloride
MgBr2 magnesium bromide
BaS Barium sulfide
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Common ions and their names
is
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Ternary ionic compounds

• Ternary ionic compounds have three elements in
  the makeup of the compound. One of the members
  in the ionic compound is a polyatomic ion.
• The overall or net charge must be zero in the
  ternary ionic compound if it is not then
  subscripts and parentheses must be used to
  balance the charge.
• Polyatomic ions with oxygen in their composition
  are called oxyanions and always are negatively
  charged.
• In naming ternary ionic compounds the ion names
  are used as in the case for binary ionic
  compounds.
• When oxyanions combine with polyvalent cations,
  the stock system must be used in the name.

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Examples of ternary ionic compounds

• Sodium ion and carbonate ion
• Na1 CO3-2
• Cross over charges Na12 CO3-21
• Na2CO3
• The name of the compound is sodium carbonate.

Iron(II) ion and sulfate ion Fe2
SO4-2 Cross over charges Fe22
SO4-22 Reduce ratios by dividing subscripts by 2.
FeSO4 The name of the compound is iron(II)
sulfate.
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Name the following compounds

• LiBr
• Lithium bromide
• Sn(NO3)4
• Tin(IV) nitrate
• FeCl2
• Iron(II) chloride
• CaS
• Calcium sulfide
• Pb(OH)2
• Lead(II) hydroxide
• Fe2(CO3)3
• Iron(III) carbonate

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Write the formula for the following

• Vanadium(V) sulfide
• V2S5
• Magnesium sulfate
• MgSO4
• Cobalt(II) bromide
• CoBr2
• Aluminum chloride
• AlCl3
• Copper(II) iodide
• CuI2
• Strontium nitrite
• Sr(NO2)2

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Acids and Bases

• Acids are ionic or polar covalent compounds that
  are dissolved in water and have hydrogen as their
  cation.
• The symbol (aq), refers to the term aqueous which
  means dissolved in water.
• Acids dissolves/corrodes metals and react with
  bases to form salts.
• Acids have a sour taste and are in the pH range
  of 1-6.
• There are two types of acids, binary acids and
  ternary acids.

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pH Scale and Water

• Is defined as
• pH - log H1
• H2O H1 OH1-

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Binary Acids

• Binary acids have hydrogen and a monatomic anion.
• When naming acids the prefix hydro- is placed
  on the element name and the ending is changed to
  -ic.
• HF (aq) hydrofluoric acid
• H2S (aq) hydrosulfuric acid
• When binary acids react with bases they often
  form binary salts.

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Ternary Acids

• Ternary acids have hydrogen and a polyatomic
  (oxyanion) anion and are dissolved in water.
• When naming ternary acids, the prefix hydro- is
  NEVER used in the name.
• The polyatomic anion determines the ending for
  the acid.
• If the polyatomic ion ends in ite, the ending is
  changed to ous.
• If the polyatomic ion ends in ate, the ending is
  changed to ic.

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Examples of Ternary Acids

• H2SO4(aq) sulfuric acid
• HNO2 (aq) nitrous acid
• HNO3 (aq) nitric acid
• H2SO3(aq) sulfurous acid

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Bases or Alkali

• Bases are ionic or polar covalent compounds that
  are dissolved in water and have the hydroxide ion
  as their anion.
• The symbol (aq), refers to the term aqueous which
  means dissolved in water.
• Bases dissolves/corrodes organic materials and
  react with acids to form salts.
• Bases have a bitter taste and are in the pH range
  of 8-14.
• Most bases are ternary compounds.

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Bases or Alkali

• Bases are very easy to name since they used the
  hydroxide ion in their structures.
• In all bases the word hydroxide is ALWAYS the
  last word in the compounds name.
• They are ternary or quaternary compounds
• NaOH(aq) Sodium hydroxide
• Fe(OH)3(aq) Iron(III) hydroxide
• Cu(OH)2(aq) Copper(II) hydroxide

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Review pH scale

• 0-6.9..acid
• 7....neutral
• 7.1-14base/alkali

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Naming molecular compounds with nonmetals in
their structure.

• Often prefixes are used in binary molecular
  compounds that have two nonmetals in their
  structures.
• Compounds such as carbon, nitrogen, sulfur, and
  phosphorus that bond with oxygen often use
  prefixes in naming the compound.
• The stock system can also be used in naming these
  compounds.
• The key concept is that these are covalently
  bonded nonmetals.

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Prefix Names

• Number Prefix
• 1 mono-
• 2 di-
• 3 tri-
• 4 tetra-
• 5 penta-
• 6 hexa-
• 7 hepta-
• 8 octa-
• 9 nona-
• 10 deca-

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Prefixes in naming Binary Compounds of Nitrogen
and Oxygen
Formula Name
Oxidation

• N2O dinitrogen monoxide (I)
• NO nitrogen monoxide (II)
• NO2 nitrogen dioxide (IV)
• N2O3 dinitrogen trioxide (III)
• N2O4 dinitrogen tetroxide (IV)
• N2O5 dinitrogen pentoxide (V)

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Prefixes in naming other binary and ternary
compounds

• NaF6 sodium hexafluoride
• P2O5 diphosphorus pentoxide
• CBr4 carbon tetrabromide
• Fe2O3 di-iron trioxide
• SnO2 tin dioxide
• Fe3(PO4)2 tri-iron diphosphate
• Cu(OH)2 copper dihydroxide

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Latin names

• Fe3 ferric
• Fe2 ferrous
• Sn2 stannous
• Sn4 stannic
• Cu2 cupric
• Cu1 cuprous
• Pb4 plumbic
• Pb2 plumbous
• Hg22 mercurous
• Hg2 mercuric
• Au1 aurrous
• Au3 aurric

Co2 cobaltous Ni2 nickelous Mn2 manganous Cr
3 chromic Sb3 stibbous Sb5 stibbic
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Naming Compounds with Latin names

• Fe2O3 ferric oxide
• SnO2 stannic oxide
• SnCl2 stannous chloride
• Fe3(PO4)2 ferrous phosphate
• Cu(OH)2 cupric hydroxide
• PbCl4 plumbic chloride
• PbCO3 plumbous carbonate
• Hg2O mercurous oxide
• HgSO4 mercuric sulfate

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Common Chemical Names
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Molar Mass of Compounds

• Molar mass is the number of grams needed in one
  mole of a compound.
• One mole is 6.022 x 1023 molecules.
• In a compound, all atoms in the compound are used
  to determine the molar mass of the compound.
• The subscripts are used in determining the molar
  mass.

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Finding the Molar Mass of a Compound

• Determine the total number of atoms for each
  element in the compound.
• Look up the atomic mass of the elements in the
  compound.
• Multiply the atomic mass of each element times
  the subscript of the element in the compound.
• Add all of the masses for each element in the
  compound to find the total.

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Example Problem 1

• What is the molar mass of FeO?
• Fe 55.8 g/mol O 16.0 g/mol
• How many atoms do you have of each element?
• Add the molar masses.55.8 g/mol16.0 g/mol71.8
  g/mol of FeO- Molar mass of this compound

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Molar mass example problem

• Find the molar mass of Fe2O3
• Determine the total number of atoms for each
  element in the compound.
• 2 Fe atoms 3 O atoms
• Look up the atomic mass of the elements in the
  compound.
• Fe 55.8 g/mol O 16 g/mol
• Multiply the atomic mass of each element times
  the subscript of the element in the compound.
• For Fe 55.8 g/atom 2 atoms 111.6 grams
• For O 16.0 g/atom 3 atoms 48.0 grams
• Add all of the masses for each element in the
  compound to find the total.
• From Fe 111.6 grams
• From O 48.0 grams Molar mass of
  Fe2O3 159.6 grams/mol

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Percent Composition Problems

• Percent Composition of Fe2O3
• Find the molar mass of Fe2O3
• Determine the percentage of each element
• Use the total gram amount of each element
• Divide by the molar mass of the compound
• Multiply times 100 to obtain percentage.
• a. Molar Mass Determination of Fe2O3
• 2- Fe atoms 3- O atoms
• Look up the atomic mass of the elements in
  the compound.
• Fe 55.8 g/mol O 16 g/mol
• Multiply the atomic mass of each element times
  the subscript of the element in the compound.
• For Fe 55.8 g/atom 2 atoms 111.6
  grams
• For O 16.0 g/atom 3 atoms 48.0
  grams
• Add all of the masses for each element in the
  compound to find the total.
• From Fe 111.6 grams
• From O 48.0 gramsMolar mass of
  Fe2O3 159.6 grams/mol
• Percentages of Composition
• Iron (Fe) 111.6 g 100
  159.6 g
  69.9

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Rationale for Empirical Formula

• Percent composition can be used to determine the
  simple whole number ratio of a chemical compound.
• An assumption is made that a 100 g sample was the
  basis of the composition.
• The mole amount of each element is determined
  from the composition data.
• A ratio of moles and proportion is used to
  determined the simple whole number ratio.
• The formula is then written using the data
  calculated.

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Empirical Formula Problem

• Steps
• Given the following percentages of composition
• 32.38 Na
• 22.65 S
• 44.99 O
• Assume element percentages are grams out of a
  total of 100 g sample.
• 32.38 Na 32.38 g Na
• 22.65 S 22.65 g S
• 44.99 O 44.99 g O
• Determine the moles of each element present
• moles of Na 32.38 g Na x 1 mol
  Na 1.408 mol Na
  22.99
  g Na
• moles of S 22.65 g S x 1 mol S
  0.7063 mol S
  32.07 g S
• moles of O 44.99 g O x 1 mol O
  2.812 mol O
• 
  16.00 g O

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Empirical Formula Problem

• Steps (cont)
• Determine the Smallest whole-number ratio of
  atoms
• 1.408 mol Na x moles Na
  1.993 moles Na 0.7063 mol S 1
  mol S 1 mol S
  
• 2.812 mol O x moles O 3.981 moles
  O 0.7063 mol S 1 mol S
  1 mol S
• Round numbers to whole numbers and write formula
  

Na2
S
O4
Metals are always written first. Most
electronegative nonmetal is written last.
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Empirical Formula Problem

• Problem 19
• Given the following percentages of composition
• 24.6 K
• 34.8 Mn
• 40.6 O
• Assume element percentages are grams out of a
  total of 100 g sample.
• 24.6 K 24.6 g K
• 34.8 Mn 34.8 g Mn
• 40.6 O 40.6 g O
• Determine the moles of each element present
• moles of K 24.6 g K x
  1 mol K 0.629 mol K
  39.1 g K
  
• moles of Mn 34.8 g Mn x 1 mol Mn
  0.633 mol Mn
  
  54.9 g Mn
• moles of O 40.6 g O x 1 mol O
  2.538 mol O
  16.00 g O

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Empirical Formula Problem

• Steps (cont)
• Determine the Smallest whole-number ratio of
  atoms
• 0.633 mol Mn x moles Mn
  1.006 moles Mn 0.629 mol K 1
  mol K 1 mol K
• 2.538 mol O x moles O 4.035
  moles O 0.629 mol K 1 mol K
  1 mol K
• Round numbers to whole numbers and write formula
  

K
Mn
O4
Potassium permanganate
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More Practice
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Answers for Homework-1
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Answers for Homework-2
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Stock system naming of compounds of Nitrogen and
Oxygen

• N2O nitrogen(I) oxide
• NO nitrogen(II) oxide
• NO2 nitrogen(IV) oxide
• N2O3 nitrogen(III) oxide
• N2O4 nitrogen(IV) tetroxide (needed)
• N2O5 nitrogen(V) oxide

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Answers for Homework-3
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More Practice

• Name the following compounds using the three ways
  covered in class
• Fe3(PO4)2
• iron(II) phosphate
• iron diphosphate
• ferrous phosphate
• Cu2SO4
• copper(I) sulfate
• copper monosulfate
• cuprous sulfate

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More Practice 2

• Name the following compounds using the three ways
  covered in class
• Ca(MnO4)2
• calcium permanganate
• Mg(NO3)2
• magnesium nitrate
• Pb(NO2)2
• lead(II) nitrite or lead dinitrite or
• plumbous nitrite

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More Practice 3

• Write the chemical formula for the compounds
  given below
• strontium bromide
• iron(II) carbonate
• lead(IV) sulfide
• barium oxide

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More Practice 4

• Write the chemical formula for the compounds
  given below
• silicon monoxide
• iron tri-iodide
• lead(II) sulfite
• sodium phosphide