1 Mr. ShieldsRegents Chemistry U09 L03

2 Stock System for Naming Ionic Compounds We’ve seen how ionic compounds form and what they are. Now Let’s see how we name them … First, There are two ways we can refer to the Oxidation number of an ion 1) as a superscript such as Fe +2 - Utilized when we write ionic formulas 2) or as a Roman numeral such as Iron (II) - Utilized when writing out the name of the compound Stock System

3 Naming Ionic Compounds When writing names of ionic compounds we need to be able to differentiate between the various oxidation states of an element. For example, look at your reference table. What is the possible oxidation states of Iron? To differentiate between these two you need a way to let the reader know which one your referring to, is it … - Iron (II) for Fe +2 or Iron (III) for Fe +3

4 Roman numerals are used when writing the name of compounds to specify the oxidation number of the cation For example: FeCl 3  Fe +3 + Cl -  Iron (III) Chloride FeS  Fe +2 + S -2  Iron (II) Sulfide Cu 2 0  Cu +1 + O 2-  Copper (I) Oxide But … AlCl 3 is simply Aluminum Chloride, not Aluminum (III) Chloride and CaCl 2 is Calcium Chloride Not Calcium (II) Chloride. WHY? LOOK at your Reference Table There is only 1 possible oxidation state for these metals

5 Binary endings Notice the endings for the names of these compounds FeCl 3 Iron (III) Chloride FeS Iron (II) Sulfide Cu 2 0 Copper (I) Oxide These are binary compounds and the endings for the compound name end in “-ide” by adding it to the stem of the anion - Chlorine becomes “Chloride” - Sulfur becomes “Sulfide” - Oxygen becomes “Oxide”

6 More than 1 Ox. State Only 1 Ox. State “-ide” endings Use Roman numerals No Roman Numerals

7 Polyatomic Name Endings Roman numerals are also used when naming Polyatomic ionic compounds For example: Cu(NO 3 ) 2  Cu +2 + NO 3 -  Copper (II) Nitrate However, the endings for these polyatomics may take Several forms: “-ide”, “-ate” or “-ite” Which ending used depends upon which polyatomic is joined to the metal.

8 Name endings can often provide information on How many oxygens are in the polyatomic. For example: ClO 2 - Chlorite(BrO 2 - = Bromite) ClO 3 - Chlorate SO 3 -2 Sulfite SO 4 -2 Sulfate NO 2 - Nitrite NO 3 - Nitrate -ate’s have more Oxygen than -ites

9 Writing Chemical Formulas – The Crisscross method The easiest way to determine a chemical formula of an ionic compounds is to use the crisscross method: 1. Determine the oxidation number of each element or polyatomic 2. This number becomes the subscript of the other ion (w/o the charge, i.e. crisscross) 3. An Oxidation number of 1 is not used as a subscript 4. Subscripts must be reduced to the smallest whole number ratio X

10 Crisscross method Crisscross method Examples of the crisscross method: Iron (II) Bromide:Fe 2+ Br 1- FeBr 2 Chromium (III) oxide: Cr 3+ O 2- Cr 2 O 3 Calcium sulfide:Ca 2+ S 2- CaS Ammonium Phosphate: NH 4 +1 PO 4 3- (NH 4 ) 3 PO 4 Smallest whole number ratio

11 Try These Name the following: CaF 2 KClO 4 CuO CrCl 3 K 2 SO 3 Write the chemical formula for the following: Chromium (II) Nitrate Calcium Acetate Iron (III) oxide Nickel (II) Phosphate Ammonium Hydroxide Calcium Fluoride Potassium Perchlorate Copper (II) oxide Chromium (III) Chloride Potassium Sulfite Cr(NO 3 ) 2 Ca(CH 3 COO) 2 Fe 2 O 3 Ni 3 (PO 4 ) 2 NH 4 OH Note that a Compound Can also be made up of Two polyatomics…