Naming a compound with only two nonmentals…1. Write the name of the first element along with the appropriate prefix.2. Write the name of the second element, modified to end in ide, along with the appropriate prefix.
Use mono- sparinglyThe prefix mono- should only be used to prevent confusion … as in CO and CO2 Carbon monoxide and carbon dioxide
You can write the formula from thename. The prefix tells the subscript. Nitrogen trichloride NCl3 Carbon tetrachloride CCl4 Diphosphorous pentoxide P 2O 5
Naming Binary CompoundsContaining a Metal and a Nonmetal
The Stock System Named for Alfred Stock, a German chemist of the nineteenth century. Add a Roman Numeral after the name of the positive element to indicate its oxidation number.
Using the Stock System:1. Write the name of the positive element2. Add a Roman numeral corresponding to the oxidation number of the positive element (if necessary)3. Write the name of the negative element, modified to end in -ide
When is the Roman Numeral Necessary? When the metal has more than one oxidation number. Metals in groups I A, II A, and III B, do not need Roman numerals. Others metals have several oxidation numbers, and need Roman numerals.
What is an oxidation number?An oxidation number is anumber that tells us how anelement combines with otherelements. For ions, the oxidation number is the ionic charge.
We can find oxidationnumbers in tables or wecan predict them using the periodic table.
What does the Roman Numeral do? The Roman numeral indicates the oxidation number on a single metal atom, and differentiates between several possible compounds. Consider: FeO and Fe2O3 Both contain iron and oxygen But, both cannot be iron oxide …
… so we use a Romannumeral to differentiate between the two compounds.
First, determine the oxidationnumber 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.
Likewise, for Fe2O3 …First, determine the oxidation numberof iron in Fe2O3 … … by starting with the negative element, find the oxidation number of the positive element.Since iron’s oxidation number is +3,Fe2O3 is named iron (III) oxide.
Remember … Only add a Roman Numeral if it is needed. It is needed when the metal has more than one positive oxidation number. If the element has only one positive oxidation number, you do not need a Roman numeral.
Writing formulas ofbinary compounds of a metal and a nonmental
The sum of the oxidationnumbers on all the atoms ina compound must equalzero. Consider iron (II) oxide. Oxygen is –2 +2 –2 = 0 and iron is +2. FeO The sum is 0.
Now consider iron (III) oxide In iron (III) oxide, +3 -2 the iron is +3 and Fe2O3 the oxygen is –2. These don’t add up to zero.
Now consider iron (III) oxide But, since there +6 -6 = 0 +3 -2 are two Fe atoms Fe2O3 and three O atoms, we can multiply to 2x3=6 get the totals. 3 x –2 = -6 Now the sum is zero.
Look at it another way: +6 –6 = 0 +6 -6 +3 +3 -2 -2 -2Fe2O3 = Fe Fe O O O
The “ic/ous” method …… is an archaic method, but still in use today by the chemical industry… uses the –ic or –ous suffixes on the name of the metal.… may use the Latin root… uses prefixes like hypo- & per-
Name and Lower Ox. Higher Ox.Latin Root Number Number iron ferrous ferricferrum Fe 2+ Fe 3+copper cuprous cupriccuprum Cu + Cu 2+mercury mercurous mercuric Hg22+ Hg2+
Higher oxidation number IC OUSLower oxidation number