Advanced Placement Chemistry

Lesson plan #4

1 class period

Inorganic Nomenclature

• The names and formulas of compounds are essential vocabulary in chemistry.
• There are now over 13 million known chemical substances. Naming them all would be a hopelessly complicated task if each had a special name independent of all others.
• The rules for chemical nomenclature are based on the division of substances into different categories.

• The major division is between organic compounds and inorganic ones.
• Organic compounds contain carbon, usually in combination with hydrogen, oxygen, nitrogen, or sulfur.
• All other compounds are called inorganic compounds.
• We will consider three categories of substances:

• Ionic compounds
• Molecular compounds
• Acids

• Positive Ions (Cations)

• Cations formed from metal atoms have the same name as the metal:

• Na⁺ sodium ion
• Zn⁺ zinc ion
• Al³⁺ aluminum ion
• Ions formed from a single atom are called monatomic ions.

• If a metal can form cations of differing charges, the positive charge is given by a Roman numeral in parenthesis following the name of the metal:

• Fe²⁺ iron(II) ion
• Fe³⁺ iron(III) ion
• Cu⁺ copper(I) ion
• Cu²⁺ copper(II) ion
• Ions with different charges exhibit different properties, such as color.

• Cations formed from nonmetal atoms have names that end in -ium:

• NH₄⁺ ammonium ion
• H₃O⁺ hydronium ion

• Negative Ions (Anions)

• Monoatomic (one-atom) anions have names formed by dropping the ending of the name of the element and adding the ending -ide.

• H^- hydride ion
• O^2- oxide ion
• N^3- nitride ion
• A few simple polyatomic anions also have names ending in -ide:
• OH^- hydroxide ion
• CN^- cyanide ion
• O₂^2- peroxide ion

• Polyatomic (many-atom) anions containing oxygen have names ending in -ate or -ite. These anions are called oxyanions. The ending -ate is used for the most common oxyanion of an element. The ending -ite is used for an oxyanion that has the same charge but one less O atom:

• NO₃^- nitrate
• NO₂^- nitrite
• SO₄^2- sulfate
• SO₃^2- sulfite
• Prefixes are used when the series of oxyanions of an element extends to four members, as with the halogens. The prefix per- indicates one more O atom than the oxyanion ending in -ate; the prefix hypo- indicates one less O atom than the oxyanion ending in -ite:

• ClO₄^- perchlorate (one more O than chlorate)
• ClO₃^- chlorate ion
• ClO₂^- chlorite ion (one less O than chlorate)
• ClO^- hypochlorite (one less O than chlorite)
• Notice that if you learn the rules just indicated, you need to know only the name for one oxyanion in a series to deduce the names for the other members.

• Anions derived by adding H⁺ to an oxyanion are named by adding as a prefix the word hydrogen or dihydrogen, as appropriate:

• CO₃^2- carbonate ion
• HCO₃^- hydrogen carbonate ion
• PO₄^3- phosphate ion
• H₂PO₄^- dihydrogen phosphate ion
• Notice that each H⁺ reduces the negative charge of the parent anion by one.

• Ionic Compounds

• Names of ionic compounds are the cation name followed by the anion name:

• BaBr₂ barium bromide
• Al(NO₃)₃ aluminum nitrate
• Cu(ClO₄)₂ copper(I) perchlorate (or cupric perchlorate)

• Acids are an important class of hydrogen-containing compounds and are named a special way.
• An acid is defined as a substance whose molecules yield hydrogen ions (H⁺) when dissolved in water.
• Acids based on anions whose name end in -die.

• Anions whose names end in -ide have associated acids that have the hydro- prefix and an -ic ending as in:

• Cl^- (chloride) HCl (hydrochloric acid)
• S^2- (sulfide) H₂S (hydrosulfuric acid)

• Acids based on anions whose names end in -ate or -ite.

• Anions whose names end in -ate have associated acids with an -ic ending, whereas anions whose names end in -ite have acids with an -ous ending. Prefixes in the name of the anion are retained in the name of the acid.

• ClO^- (hydochlorite) HClO (hypochlorous acid)
• ClO₂^- (chlorite) HClO₂ (chlorous acid)
• ClO₃^- (chlorate) HClO₃ (chloric acid)
• ClO₄^- (perchlorate) HClO₄ (perchloric acid)

• The procedures used for naming binary (two-element) molecular compounds are similar to those used for naming ionic compounds.

• The name of the element farthest to the left in the periodic table is usually written first.
• If both elements are in the same group in the periodic table, the lower one is named first.
• The name of the second element is given an -ide ending.
• Greek prefixes are used to indicate the number of atoms of each element. The prefix mono- is never used with the first element. When the prefix ends in a or o and the name of the second element begins with a vowel, the a or o is often dropped.