Naming and Formula Writing

“The sum of the oxidation numbers must equal zero.” You need to learn the majority of the symbols and charges on the oxidation number sheet

Naming: The basics For those elements and ions whose oxidation numbers that do not vary, simply name the positive ion and then the negative one and You are done. Example NaCl is Sodium Chloride.

Traditional (old) system: Is used with those metallic elements that can have more than one oxidation number. That would be most of the “d” block metals.

FeCl 2 is Ferrous Chloride Use the ion whose oxidation number does not change to determine which form of iron was used. Since chlorine is always anegative one and there are two chlorine atoms in the formula, the iron must be the plus two variety because the sum of the oxidation numbers must equal zero. This form of iron is called Ferrous thus the name is Ferrous Chloride.

Stock System: Is used with the same elements as the tradition system, and iseasier to use when going from name to formula. In this system FeCl 2 would be Iron II Chloride

The oxidation number of iron is determined the same as above however in this system a roman numeral is used to denote the Oxidation number of the metal instead of the “ic” or “ous”ending. Do not use roman numerals with elements who’s oxidation numbers don’t vary.

Binary Naming: Is used with binary compounds (containing only two elements) Both of whose oxidation numbers can vary. That makes determining the oxidation numbers of each difficult. There are five simple steps to this system.

As 2 O 5 Is Diarsenic pentoxide 1. Prefix for the number of atoms of the first element. In is example its “Di” (never use the prefix mono For the first element.) It is considered redundant. 2. The full name of the first element “arsenic” 3. Prefix for the number of the atoms of the second element “pent” (There must be a prefix before the second element.) 4. The root of the name of the second element. “ox” 5. Add the ending “ide” and it’s done Di arsenic pent ox ide

The prefixes One = mono Two = di Three = tri Four = tetra Five = penta Six = hexa Seven = hepta Eight = octa Nine = nona Ten = deca

Formula writing is the reverse: Calcium Nitrate is Ca (NO 3 ) 2 Ca is a +2 and NO 3 is a -1 so two NO 3 groups are needed to make the sum of the oxidation numbers equal zero. To show that put the NO 3 group in parenthesis and add the subscript 2

I recommend that you write in the charges when you write formulas it will help you learn the charges and prevent careless mistakes. Ca +2 (NO 3 -1 ) 2

Use the criss-cross method to determine the subscript numbers. It works most of the time, but always check for the common denominator. Page 233 Chemistry Prentice Hall

The old system Ferric Sulfate With the old system you have to know that Ferric is Fe +3 andthat sulfate is SO 4 -2 in order to start. So you need to know the oxidation sheet. Again the oxidation numbers must equal zero. To do that the common denominator of 6 is required. Again criss-cross 2 x 3 = 6 and 3 x 2 =6 Fe +3 2 (SO 4 -2 ) 3

Stock system Iron III Sulfate is the same as above except that you are told in the name that iron is a + 3 so you did not have memorize that detail. Fe +3 2 (SO 4 -2 ) 3 The roman numeral III is the + 3 by the iron.

Binary System Dinitrogen Trioxide Just write down what the name says. Two nitrogen and three oxygen N 2 O 3