Chapter 7
Chemical Formulas and Chemical Compounds

  1. Introduction Chemical Names and Formulas
    1. common names vs IUPAC system of naming
    2. calcium carbonate = limestone
    3. sodium chloride = table salt
    4. hydrogen oxide = water
  2. Significance of a Chemical Formula
    1. ionic v molecular formula -- ratio of elements v actual number in molecules
    2. symbol - name of element
    3. subscript - number of that element present in the formula
    4. use of parentheses
    5. significance of no subscript
  3. Monatomic Ions
    1. ions are charged particles formed from elements by the loss or gain of electrons
    2. monatomic ions - definition
    3. number gained or lost for main group elements usually determined by electron configuration and octet rule
    4. notable exceptions are carbon and silicon, tin and lead
    5. d block elements (transition elements) can form +2 and +3 (e.g. iron and chromium) or sometimes +1 and +4 ions.
    6. vanadium and lead form ions with charges of +2, +3 and +4
      1. Naming Monatomic Ions
        1. for anions name of element modified to have ending -ide e.g. chlorine becomes chloride; fluorine becomes fluoride
        2. for cations, the name of the ions is the same as the name of the ion
  4. Binary Ionic Compounds
    1. binary compounds - definition
    2. total positive must equal total negative e.g. Mg+2 and Br-1 produces the formula MgBr2
    3. cross over method
    4. cations always written first then anion
    5. cross over charges using absolute value for the charges
    6. check subscripts and reduce to lowest whole number ratio
    7. eliminate charges
    8. e.g. Al+3 and O-2
  5. Naming Binary Ionic Compounds
    1. naming system = nomenclature
    2. combine name of cation and name of anion
    3. in binary compounds the name of the anion always ends in -ide
    4. name the elements as you see them
    5. e.g. Al2O3 is aluminum oxide

      Homework: Chapter 7, 7.1


      1. Stock System of Nomenclature
        1. for compounds that have an ion that can have more than one charge e.g. Fe or Cu or Hg
        2. use name of cation followed by Roman Numeral in parentheses followed by name of anion (use ide if binary compound)
        3. e.g. CuCl2 is copper (II) chloride

          Homework: Chapter 7, 7.2
      2. Compounds Containing Polyatomic Ions
        1. most polyatomic ions are anions
        2. most of these are oxyanions - definition
        3. names of oxyanions
          1. nitrate v nitrite
          2. also hypochlorite, chlorite, chlorate, perchlorate
        4. named the same as binary compounds i.e. name of cation followed by name of polyatomic anion
        5. e.g. Al2(SO4)3 is aluminum sulfate
  6. Naming Binary Molecular Compounds
    1. composed of molecules not ions as above
    2. two different systems a) Stock system and system that uses Greek prefixes
    3. prefixes indicate the subscript
    4. rules for binary compounds still apply
    5. generally, the less electronegative element is written first
    6. table 7-3 page 212 need to know
    7. Methodology
      1. compound involves two nonmetals, generally
      2. prefix + name for first element (no prefix if subscript is one)
      3. prefix + name for second element -- use ending -ide if the compound is binary
      4. Alternate way is to use the Stock System (use of Roman numerals to indicate the charge of the cation -- do not mix with Greek prefixes)
    8. table 7-4 page 213

      Homework: Chapter 7, 7.3 and 7.4
  7. Covalent Network Compounds
    1. all atoms joined to other atoms by covalent bonds -- no molecules
    2. subscripts indicate ratio just as in ionic compounds
    3. nomenclature is same as for molecular compounds
    4. e.g. SiC, SiO2, and Si3N4
  8. Acids and Salts
    1. acids are molecular compounds
    2. formula usually begins with the element hydrogen
    3. acids usually either binary acids or oxyacids
    4. binary acid - definition
    5. oxyacid - definition
    6. all acids are solutions of the compound in water -- often have he subscript (aq) after the formula
    7. many of our polyatomic ions come about when an oxyacid loses its hydrogen
    8. table 7-5 page 214
    9. salt - definition
    10. the anion of the acid may have no hydrogen or some hydrogen from the oxyacid

      Homework: 7.5

      Naming Compounds: flowchart
  9. Oxidation Numbers
    1. oxidation number (oxidation state) - definition
    2. applies to molecular compounds -- often used to indicate the charge of an ion
    3. need to know for writing formulas, naming compounds, and balancing equations
      1. Assigning Oxidation Numbers
        1. eight rules on page 216
        2. e.g. water
        3. e.g. hydrogen fluoride
        4. e.g. UF6
        5. e.g. H2SO4
        6. e.g. ClO31-

          Homework: Chapter 7, 7.6
      2. Using Oxidation Numbers and Formulas and Names
        1. many elements have multiple oxidation states
        2. table 7-6 page 219
        3. the Roman numerals in the Stock system represent the oxidation numbers of the elements
        4. can use the stock system to replace the prefix system
        5. table on page 219 -- prefix v stock system

          Homework: Chapter 7, 7.7


  10. Using Chemical Formulas
    1. Intro
      1. formula indicates the elements present and the relative number of atoms or ions
      2. use formulas to calculate formula mass, molar mass, and percentage composition by mass of a compound
    2. Formula Masses
      1. formula mass - definition
      2. e.g. Water
      3. e.g. sodium chloride
      4. e.g. potassium chlorate

        Homework: Chapter 7, 7.8
    3. Molar Mass
      1. molar mass of a compound - definition
      2. e.g. barium nitrate

        Homework: Chapter 7, 7.9

    4. Molar Mass as a Conversion Factor
      1. relates amount in moles to a mass in grams
      2. can go from moles to number of atoms or molecules using Avogadro’s number and visa versa
      3. can go from grams to atoms or molecules using Avogadro’s number and visa versa
      4. e.g. page 225 Sample problem 7-9 sections a and b

        Homework: Chapter 7, 7.10

    5. Percentage Composition
      1. percentage composition - definition
      2. e.g. Sample Problem 7-10 Cu2S
      3. e.g. Na2CO3 . 10H2O

        Homework: Chapter 7, 7.11
  11. Determining Chemical Formulas
    1. Introduction
      1. new compounds are analyzed to determine its percentage composition
      2. from percentage composition data, the empirical formula can be calculated
      3. empirical formula - definition
    2. Calculation of Empirical Formulas
      1. convert percentages given to grams -- assuming a 100 gram sample
      2. convert grams to moles
      3. make the moles the subscripts
      4. reduce the subscripts to lowest whole number ratio
        1. can be done by dividing all subscripts by the smallest subscript
        2. keep in mind that because of rounding and experimental error the mole ratios may not appear to be whole number ratios
      5. e.g. Sample Problem: The percentage composition of diborane is 78.1% Boron and 21.9% hydrogen. Calculate its empirical formula.

        Homework: Chapter 7, 7.12
    3. Calculation of Molecular Formulas
      1. an empirical formula may be the correct formula for an ionic compound or a network covalent compound but not for a covalent compound e.g.. the correct formula for diborane is B2H6 since it is a molecular formula; its empirical formula is BH3 as we calculated.
      2. to calculate the molecular formula you need
        1. the empirical (simplest formula) or the percentage composition of the compound so you can calculate the empirical formula
        2. the molecular mass of the compound
      3. when calculating the molecular formula you will use the methodology
        (molar mass of the empirical formula) times x = molar mass of cpd
      4. e.g. Sample problem 7-14 page 232

        Homework: Chapter 7, 7.13

end of notes

 

A monatomic ion is an ion formed from a single atom. back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A binary compound is a compound composed of two different elements. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Oxyanions are polyatomic ions that contain oxygen. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A binary acid is an acid that consists of hydrogen and one other element. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An oxyacid is an acid that contains hydrogen, oxygen and one other element. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A salt is an ionic compound composed of a cation and the anion from an acid. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An oxidation number (oxidation state) indicates the general distribution of electrons among the bonded atoms in a molecular compound. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The molar mass is numerically equal to its formula mass. Back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Percentage composition is the percentage by mass of each element in a compound.back

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

An empirical formula consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole number ratio of the different atoms in the compound.back