Naming Compounds and Writing Formulas Chapter 2 (2.6 and 2.7)

Writing Names for Ionic Compounds Write the name of the cation followed by the name of the anion Ending of monatomic anions must be changed to –ide Include Roman numerals for metals that have variable charges Groups 1 & 2, Al, Zn, Ag, Cd do not need Roman Numerals

Naming Hydrates The ONLY time that you use the numerical prefixes with ionic compounds is to indicate the number of water molecules attached to a hydrated ionic compound CuSO 4. 5H 2 O copper (II) sulfate pentahydrate

Oxides (O 2- ) Metals and nonmetal combine with oxygen to form oxides Examples: CaO is calcium oxide PtO 2 is platinum (IV) oxide

Peroxides (O 2 2- ) Active metals (group 1 except Li, group 2 except Be & Mg) may combine with oxygen to form peroxides Each oxygen is 1- Example: CaO 2 is calcium peroxide H 2 O 2 is hydrogen peroxide; H can act as an active metal

Superoxides (O 2 - ) Very active metals (K, Rb, Cs) may combine with oxygen to form superoxides Each oxygen is -1/2 Example: RbO 2 is rubidium superoxide

Name these Oxides KO 2 K 2 O 2 K 2 O potassium superoxide potassium peroxide potassium oxide

Names and Formulas for Binary Molecular Compounds Binary molecular compounds contain two elements. The most metallic element (i.e., the one farthest to the left on the periodic table) is usually written first. Exception: NH 3 (ammonia) If both elements are in the same group, the lower one is written first. Example: SO 2

Greek prefixes (page 63) are used to indicate the number of atoms (mono, di, tri). The first letter is omitted when o-o or a-o combinations occur. The prefix mono is never used with the first element (Example: carbon monoxide, CO). Examples: Cl 2 Odichlorine monoxide N 2 O 4 dinitrogen tetroxide NF 3 nitrogen trifluoride P 4 S 10 tetraphosphorus decasulfide

Writing empirical formulas for ionic compounds You must combine cations and anions in a ratio so that the total positive charge is equal to the total negative charge Use the criss cross method

Binary Ionic Compounds Contain atoms of two elements Write the chemical formula by using the criss cross method CaI 2

Subscripts must be reduced since an empirical formula shows the lowest whole number ratio of ions or atoms Ca 2 O 2 must be reduced to CaO

Ternary Ionic Compounds Contain atoms of three elements Parentheses must be placed around polyatomic ions to separate the ion from the subscript when more than one ion is needed Ca(OH) 2

Charges of Ions GroupCharge

Names and Formulas of Acids The names of acids are related to the names of anions: -ide becomes hydro-...-ic acid; HCl hydrochloric acid -ate becomes –ic acid; HClO 4 perchloric acid -ite becomes –ous acid. HClO hypochlorous acid