Nomenclature and Writing Formulas Rules to Follow

Writing Formulas Ionic Compounds: –Look at charge on cation and charge on anion –Example: Magnesium bromide Charges need to cancel out so… 1 Mg (+2) needs 2 Br (-1) MgBr 2

Formulas/Names with Metals Cation (+) first, anion (-) second. Cation name comes directly from the Periodic Table. Anion name: Change the end of the element name to –ide. Example: Na 2 S Sodium sulfide

Formulas/Names with Polyatomic Ions Names of polyatomic ions do not change. Formulas for polyatomic ions do not change. You need to recognize that a polyatomic ion exists and then use the chart to determine its name.

If you need to add subscripts, protect the polyatomic ion with ( ). If you don’t need subscripts, do not use ( ). Example: Pb(NO 3 ) 2 Lead nitrate NaOH Sodium hydroxide

Formulas/Names with Metals of Variable Charges (Follow rules for compounds with metals) Cation (+) first, anion (-) second. Cation name comes directly from the Periodic Table, with this exception: determine the charge of the cation and use Roman numerals after name to show the charge. Anion name: Change the end of the element name to –ide.

These are the metals that you need to recognize as having variable charges: Copper, Iron, Mercury, Lead, Tin, Manganese, Cobalt, Gold and Chromium. Example: CuCl 2 Copper (II) chloride

Formulas/Names with 2 Nonmetals (Almost the same rules as formulas with metals with one addition.) Cation (+) first, anion (-) second. Cation name comes directly from the Periodic Table. Anion name: Change the end of the element name to –ide. Put Greek prefixes before names of elements to show subscript. With cations do not use prefix “mono-“, but you do use the prefix mono for anions.

Prefixes: Onemono- Twodi- Threetri- Four-tetra- Fivepenta- Sixhexa- Sevenhepta- Eightocta- Ninenona- Tendeca- Example: ClO 2 Chlorine dioxide