Chapter 7

CHEMICAL NAMES AND FORMULAS

Objectives

Explain the significance of a chemical formula

Determine the formula of an ionic compound formed between two given ions.

Name an ionic compound given its formula.

Using prefixes, name a binary molecular compound from its formula.

Write the formula of a binary molecular compound given its name.

  1. Section 7-1 (Chemical names and formulas)
    1. Significance of a chemical formulas
      1. Molecule
        1. Molecular formula- shows number of atoms of each element contained in a single molecule of a compound.
        2. Subscripts tell the number of atoms
      2. Ionic compound- consist of a crystal lattice
        1. Formula unit- the simplest ratio of the compound’s positive and negative ions
        2. Subscripts tell the number of ions needed to balance.
        3. Subscript outside parentheses multiplies thru everything inside the parentheses.
      3. Naming monatomic ions
        1. Cations
          1. S-block elements
            1. Positive
            2. Take their name plus the word ion
            3. Sodium becomes sodium ion
          2. D-block elements
            1. Positive
            2. Take a roman numeral to indicate the charge.
            3. Iron II or Iron III
        2. Anions
          1. Negative
          2. Take an –ide ending
          3. Chlorine becomes chloride
      4. Writing Binary Ionic compounds
        1. Definition- compounds composed or two different elements
        2. Steps
          1. Write the symbols of the ions

            2. Mg+2 N-3

          2. Cross over the charges by using absolute value of each ion’s charge as the subscript for the other ion.

            3. Mg3+2 N2-3

          3. Check subscripts and divide them by their largest common factor.

        Mg3N2

      5. Naming Binary Ionic compounds
        1. Nomenclature or naming system
        2. S-block elements
          1. cation takes its name
          2. anion take an -ide ending
        3. D-block elements- use the stock system
          1. cation takes a roman numeral to indicate its charge.
          2. Anion takes an –ide ending
        4. Compounds containing Polyatomic ions
          1. All but ammonium are negative
          2. Most are Oxyanions-
            1. Ones that contain oxygen
            2. May contain different amounts of oxygen
              1. prefix (hypo)- less than (ite)
              2. ite- less than ate
              3. ate- one more than ite
              4. Prefix (per)- one more than -ate
    2. Naming Binary Molecular compounds
      1. The less electronegative element is first and is given a prefix only when it contributes more than one.
      2. The second element is always given a prefix and an –ide ending.
      3. The o or a at the end of a prefix is usually dropped when the work following the prefix begins with another vowel.
      4. Table of numerical prefixes. 7-3
        5.

        Number

        Prefix
           
           
           
           
           
           
           
           
           
           

      5. Ex.
    3. Naming Acids and Salts
      1. Acids
        1. A compound that contains a hydrogen
        2. Binary acids
          1. Use a hydro- prefix and an -ic ending
          2. Attach the word acid at the end
        3. Oxyacids
          1. Use an -ic ending when polyatomic ends with -ite ending.
          2. Use an -ous ending when polyatomic ends with -ate.

     

     

     

     

     

     

     

     

     

     

     

     

    Objectives

    List the rules for assigning oxidation numbers.

    Give the oxidation number for each element in the formula of a chemical compound.

    Name binary molecular compounds using oxidation numbers and the stock system.

  2. Section 7-2 (Oxidation numbers)
    1. Assigning Oxidation numbers
      1. The oxidation number is it charge and is based on its electronegativity
      2. The book list 8 rules on page 216 we will condense the list.
        1. Atoms in a pure element have an oxidation of zero
        2. More-electronegative have a negative charge equal to its anion.
        3. Less-electronegative have a positive charge equal to its cation.
        4. Non-metals can have positive oxidation numbers.
        5. Hydrogen has a negaive oxidation when with metals
        6. The algebraic sum must be zero or the charge of the polyatomic ion
    2. Using oxidation number for formulas and names- elements can have different number of valence electrons

    Objectives

    Calculate the formula mass or molar mass of any given compound.

    Use molar mass to convert between mass in grams and amount in moles of a chemical compound.

    Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound.

    Calculate the percentage composition of a given chemical compound.

  3. Section 7-3 Using Chemical Formulas
    1. Formula Masses
      1. Definition-of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula.
        1. Take the average atomic mass off periodic table
        2. Multiply by the subscript
        3. Add to get total
        4. Practice PG 25

         

         

         

      2. Molar masses- is the numerically equal to its formula mass.
      3. Molar mass as a conversion factor
        1. Conversion factor must equal one
        2. One mole equals the formula mass
        3. Practice PG 226

         

         

         

         

      4. Percentage composition
        1. Allows one to determine the amount of a given part of a compound
        2. (Part / whole) X 100 %
        3. Practice PG 227

     

     

     

     

     

     

     

     

    Objectives

    Define empirical formula, and explain how the term applies to ionic and molecular compounds.

    Determine an empirical formula from either a percentage or a mass composition.

    Explain the relationship between the empirical formula and the molecular of a given compound.

    Determine a molecular formula from an empirical formula.

     

  4. Section 7-4 Determining Chemical Formulas
    1. Calculation of empirical formulas
      1. Definition- consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole-number mole ratio of the different atoms in the compound.
      2. Starting with percentage measurements.
        1. Assume you have 100 grams
        2. Convert the percentages to mass numbers
        3. Divide by the molar mass
        4. Divide the answer by the smallest number to get lowest ratio
        5. Round each number in the ratios to the nearest whole number yields the correct mole ratio.
      3. Practice PG 230
    2. Calculation of Molecular Formulas
      1. Empirical is the smallest ratio
      2. Molecular formula is the actual amount
        1. Fist determine the empirical formula
        2. Determine the ratio of molecular mass (a given) to empirical formula mass.
        3. Multiply the empirical formula’s subscripts by the ratio.
        4. Write the molecular formula
        5. Practice PG 233