Naming Binary Compounds Containing a Metal and a Nonmetal Pisgah High School M. Jones

The Stock System Add a Roman numeral after the name of the metal to indicate the oxidation number. Named for Alfred Stock, a German chemist and teacher who published the system in 1919.

Using the Stock System: 1.Write the name of the metal 2.Add a Roman numeral corresponding to the oxidation number of the metal (if necessary) 3.Write the name of the negative element, modified to end in -ide

When is the Roman Numeral Necessary? In addition, omit the Roman numeral for Al, Ga, In, Zn, Cd and Ag. Metals in groups IA, IIA, and III B do not need Roman numerals. When the metal has more than one oxidation number.

What is an oxidation number? The oxidation number is a number that tells us how an element combines with other elements. For ions, the oxidation number is the ionic charge.

What does the Roman Numeral do? Consider: FeO and Fe 2 O 3 Both contain iron and oxygen But, both cannot be iron oxide … The Roman numeral indicates the oxidation number on a single metal atom, and differentiates between several possible compounds.

What does the Roman Numeral do? Consider: FeO and Fe 2 O 3 Both contain iron and oxygen But, both cannot be iron oxide … Therefore… FeO is called iron(II) oxide and Fe 2 O 3 is called iron(III) oxide.

First, determine the oxidation number of iron in FeO … … by starting with the negative element, find the oxidation number of the positive element. Since iron has an oxidation number of +2, FeO is named iron(II) oxide.

First, determine the oxidation number of iron in Fe 2 O 3 … … by starting with the negative element, find the oxidation number of the positive element. Since iron’s oxidation number is +3, Fe 2 O 3 is named Then for Fe 2 O 3 … iron(III) oxide.

Remember … You need not use a Roman numeral for metals in groups IA, IIA and IIIA, or for Al, Ga, In, Zn, Cd or Ag The Roman numeral indicates the oxidation number of the metal.

Name these compounds: SrO CrCl 3 ZnS Mn 2 O 3 SnF 4 TiS 2 Srontium oxide Chromium(III) chloride Zinc sulfide Manganese(III) oxide Sin(IV) fluoride Titanium(IV) sulfide

Writing formulas for binary compounds of a metal and a nonmetal

The sum of the oxidation numbers on all the atoms in a compound must equal zero. FeO +2 –2 = 0 Consider iron(II) oxide. The sum is 0. Oxygen is –2 and iron is +2.

Now consider iron(III) oxide Fe 2 O In iron(III) oxide, the iron is +3 and the oxygen is –2. These don’t add up to zero.

Now consider iron(III) oxide Fe 2 O = 0 But, since there are two Fe atoms and three O atoms, we can multiply to get the totals. 2 x 3 = 6 3 x –2 = -6 Now the sum is zero.

Look at it another way: Fe 2 O 3 = Fe Fe O O O –6 = 0

Now you are ready to write formulas

The Crisscross Method Be aware of the potential problems with this method. …most of the time. Simple but effective…

Suppose you are writing the formula for copper(II) chloride First, write down the symbols : CuCl

Then write the oxidation numbers in copper(II) chloride CuCl The oxidation number of copper comes from the name. +2 Get the oxidation number of chlorine from the periodic table.

Crisscross the numbers for the formula of copper(II) chloride CuCl When you crisscross, ignore the signs.

1 Clean up the subscripts in the formula of copper(II) chloride CuCl +2 2 Subscripts of 1 are invisible. (don’t even put the 1)

Cu Clean up the subscripts in the formula of copper(II) chloride Cl +2 2 Subscripts of 1 are invisible. (don’t even put the 1)

Now you have the formula of copper(II) chloride CuCl 2

When is the “crisscross method” a problem? When all the subscripts are divisible by a number other than 1.

Look at chromium(VI) oxide CrO Oxygen is always The oxidation number of Cr is +6

CrO Look at chromium(VI) oxide When you crisscross, both subscripts are divisible by 2. Now, crisscross the oxidation numbers.

Cr __ 2__ 2 Look at chromium(VI) oxide Divide each subscript by 2. O 62

O Look at chromium(VI) oxide 3 This is the correct formula Remember, 1’s are invisible. Cr

Remember: reduce the subscripts to their smallest whole-number values. Unless there’s a really good reason not to.

Some Exceptions: N2O4N2O4N2O4N2O4 Hg 2 Cl 2 C2H6C2H6C2H6C2H6 C6H6C6H6C6H6C6H6 H2O2H2O2H2O2H2O2 P 4 O 10

The “ic/ous” System

The “ic/ous” method … … uses prefixes like hypo- & per- … may use the Latin name … uses the –ic or –ous suffixes on the name of the metal. … is an archaic method, but still in use today by the chemical industry

IC OUS Higher oxidation number Lower oxidation number Use “ic” for the higher oxidation number, like ferric. Use “ous” for the lower oxidation number, like ferrous.

Name and Latin Root Lower Ox. Number Higher Ox. Number ironferrumferrous Fe 2+ ferric Fe 3+ coppercuprumcuprous Cu + cupric Cu 2+ mercurymercurous Hg 2 2+ mercuric Hg 2+

Examples … FeCl 2 CuOFeN Cu 3 P HgS Hg 2 Cl 2 Ferrous chloride Cupric oxide Ferric nitride Cuprous phosphide Mercuric sulfide Mercurous chloride

Write the formula … Ferric bromide Cupric nitride Ferrous chloride Mercuric oxide Mercurous iodide Stannous fluoride FeBr 3 Cu 3 N 2 FeCl 2 HgO Hg 2 I 2 SnF 2

Mike Jones Pisgah High School Canton NC Copyright 2012 All rights reserved.