Formulas and Nomenclature Type 1 Type 2 Type 3

Type 1 Binary Ionic Compounds Binary ionic compounds contain a positive ion (cation)which is always written first in the formula and followed by a negative ion (anion). (The Type 1 metal present forms only a single cation. This means the metals only has one charge or oxidation state.)

Writing Binary Ionic Formulas Writing Binary Ionic Formulas is very simple. If the oxidation numbers or charges of the ions do not balance each other out, we “criss-cross”. Example: Na+ S2- (these do not balance!) Na+ S2- Na2S (when the charges balance, the formula is complete)

Type 1– Binary Ionic Nomenclature Rules for naming binary ionic formulas 1st elements always says its complete name 2nd element drops ending (uses only the word root) and adds an –ide ending Example: KCl – Potassium chloride

Type II Binary Ionic Compounds Type II binary ionic compounds contain metals that have more than one type of cation. Example: Fe 2+ and Fe3+ Both ions are iron but with different oxidation numbers.

Writing formulas for Type II Binary Ionic Compounds These formulas are written exactly like Type I formulas. If the oxidation numbers do not balance out, you “criss-cross” the charges to form subscripts. Fe2+ Cl-  FeCl2

Type II Binary Ionic Compounds Nomenclature Rules: Cation says its full name Oxidation number is given in Roman numerals after the cation’s name Anion drops its ending (to the word root) and adds an –ide ending

Nomeclature for Type II Binary Ionic Compounds Examples: FeCl2 -- Iron (II) chloride Cu3N2 -- Copper (II) nitride

You don’t know the “charge” of the cation? If you do not know the oxidation number of the cation, you can determine the “charge” by doing a little algebra. Determine the charge of the anion, then multiply the anion’s charge by the subscript. Take that number and divide by the cation’s subscript. This will determine the oxidation number of the cation.

Special names for Type II Cations Some Type II cations have a name using the “old” system as well as the “new system”. The old system, still widely used, adds to the root or stem of the Latin name of the metal the suffixes –ous and –ic. These represent the lower and higher charges respectively.

Old Names for Type II ions Old System New System Fe2+ Ferrous Iron (II) Fe3+ Ferric Iron (III) Cu+ Cuprous Copper (I) Cu2+ Cupric Copper (II) Sn2+ Stannous Tin (II) Sn4+ Stannic Tin (IV)

Two Polyatomic Ions with “Old System” Names New System NH4+ Ammonium Hg22+ Mercurous Mercury (I)

Writing Ternary Ionic Compound Formulas Ternary Ionic Formulas are formed with a cation or an anion with two or more elements present. We call these anions POLYATOMIC. Polyatomic ions may be used with either Type I or Type II ions.

Writing Formulas with Polyatiomic Ions Formulas are written like Type I or Type II ions. If the oxidation numbers or charges do not balance, you “Criss-Cross”.

Writing Formulas with Polyatomic Ions Examples: Pb2+ PO43- (the charges do not balance) Pb2+ PO43- Pb3(PO4)2 The polyatomic ions is in parentheses whenever a subscript is added.

Naming Ternary Ionic Formulas Nomenclature rules: The Type I cation says its complete name, Type II cations give charge or use old system of naming The polyatomic says its complete name

Ternary Ionic Compounds Examples: PbSO4  lead (II) sulfate The charge on sulfate is a 2-, therefore the charge on the lead must be a 2+.

Type III Binary Covalent Formulas Type III compounds are nonmetal—nonmetal covalent compounds. In order to form these compounds, we cannot use charges to predict the formula because the valence electrons are not transferred from one element to another like ionic compounds. These elements share.

Binary Covalent Compounds In order to name the binary covalent compound, we must use prefixes to tell how many of each different element is used in the compound. You NEVER criss-cross charges with covalent compounds.

Greek Prefixes for Covalent Compounds mono –1 di – 2 tri –3 tetra – 4 penta -- 5 hexa – 6 hepta – 7 octa– 8 nona– 9 deca-- 10

Binary Covalent Compounds Nomenclature rules for Binary Type III compounds: The first element in compound is named first, using the full element name. The second element is named as if it were an anion (--ide ending) Prefixes are used to denote the numbers of atoms present. The Prefix mono is NEVER used for naming the first element.

Naming Binary Covalent Compounds Example: CCl4 -- Carbon tetrachloride 1st element is carbon 2nd element is chlorine (drops –ine and replaces with –ide) 2nd element receives prefix denoting number of chlorine atoms NOTE: mono was not used with 1st element!

Nomenclature continued Example: N2O – dinitrogen monoxide 1st element says its name 2nd element drops ending and adds –ide Prefixes are used with both elements to denote quantity in molecule dinitrogen monoxide (prefixes are underlined only for emphasis)

How do I write the formula from the name? In Type III compounds, writing the formula from the name is very simple. The prefix tells you exactly how many of each element is present. Example: Dinitrogen pentoxide N2O5