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- Nomenclature -
Naming Chemical Compounds
An Internet Review Lesson

Table of Contents

General Information
Ionic Formulas
   Binary
   Polyatomic
   Multiple Valence Numbers
Binary Molecular Formulas
Acids
Practice
Naming Quiz

General Information

Scientist all around the globe use a standard method for naming chemical compounds. The standards were set up by an international committee sponsored by the IUPAC. Having this standard makes life easier for people who use these compounds everyday. It would be tough to set up any experiment if scientists everywhere used different names for the same compound. It would also make the lab a much more dangerous place. Although there are other types of compounds, for this lesson we will concentrate on ionic formulas, both binary and polyatomic, binary molecular formulas, and the formulas for acids.

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Ionic Formulas

Ionic formulas are constructed of particles with opposite charges. The positive particles are referred to as the cations, the negatively charged particles are the anions. For this section, three types of ionic formulas will be discussed.

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Binary Ionic Formulas - Binary formulas contain two elements. For binary ionic formulas, the first element in the formula will be the cation and second element will be the anion. An easy way to recognize this type of formulas, is that the first element will be a metal and the second element will be a nonmetal. So, in general, the first element in the compound will come from the left side of the periodic table and the second element will be from the right side. To name a binary ionic compound you will consider the cation and anion separately. The name of the cation is the regular name of the element.
The ending of the anion is changed to -ide.

Examples:

NaCl	- sodium chloride
MgO	- magnesium oxide
CaBr2	- calcium bromide

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Polyatomic Formulas - Polyatomic ions are made from more that one atom. This group of atoms act together as one unit with a single charge. Each of the polyatomic ions have a unique name.

Table of Polyatomic Ions

1+	1-	2-	3-
ammonium , NH₄ ⁺	acetate, C₂H₃0₂^-	carbonate, CO₃^2-	phosphate, PO₄^3-
	bicarbonate, HCO₃^-	chromate,CrO₄^2-
	bisulfate, HSO₄ ^-	dichromate,Cr₂O₇^2-
	bisulfite, HSO₃ ^-	oxalate,C₂O₄^2-
	chlorate,ClO₃^-	peroxide,0₂^2-
	chlorite,ClO₂^-	silicate,SiO₃^2-
	cyanide,CN^-	sulfate,SO₄^2-
	hydroxide,OH^-	sulfite,SO₃^2-
	hypochlorite,ClO^-	tartrate,C₄H₄0₆^2-
	iodate,IO₃^-	thiosulfate,S₂O₃^2-
	nitrate,NO₃^-
	nitrite,NO₂^-
	perchlorate,ClO₄^-
	permanganate,MnO₄^-

Most of the polyatomic ions are anions. The formula for the compound will contain both a cation and an anion to balance the overall charge of the compound. The cation is named normally and the anion is given the name of the actual anion. An easy way to recognize these formulas is the fact that they are made up of more that two elements and, usually, the first element is a metal.

Examples:

Al(C₂H₃O₂)₃	- aluminum acetate	KCN	- potassium cyanide
BaSO₃	- barium sulfate	CaSO₃	- calcium sulfite
Li₃PO₄	- lithium phosphate	NH₄OH	- ammonium hydroxide

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Multiple Ionic Charges - The ionic charges of several transition metals are variable. For example the copper ion can either be 1+ or 2+.

Table of Metal Ions with Multiple Valence Numbers

antimony (III)	- Sb³⁺	iron (II)	- Fe²⁺	mercury (I)	- Hg₂⁺²
antimony (IV)	- Sb⁵⁺	iron (III)	- Fe³⁺	mercury (II)	- Hg²⁺
chromium (II)	- Cr²⁺	lead (II)	- Pb²⁺	nickel (II)	- Ni²⁺
chromium (III)	- Cr³⁺	lead (IV)	- Pb⁴⁺	nickel (III)	- Ni³⁺
copper (I)	- Cu ⁺	manganese (II)	- Mn²⁺	tin (II)	- Sn²⁺
copper (II)	- Cu²⁺	manganese (IV)	- Mn⁴⁺	tin (IV)	- Sn⁴⁺

The name of the compound should have a roman numeral placed between the name of the cation and the anion to indicate the specific charge of the cation being used. To determine this charge you need to determine what charge is needed to balance the overall compound. To do this multiply the charge of the anion by the number of anions divide this by the number of cations. This will give the charge for the cation.

Examples:

FeO	- iron II Oxide	PbO	- lead II oxide
Fe₂O₃	- iron III oxide	PbO₂	- lead IV oxide
CuOH	- copper I hydroxide	CrNO₃	- chromium II nitrate
Cu(OH)₂	- copper II hydroxide	CrNO₂	- chromium II nitrite

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Binary Molecular Formulas - Molecules are compounds that use covalent bonds to join two atoms together. Binary molecules will only have two elements in their formula. An easy way to determine if the compound is named in this manner, is the fact that the two elements in the formula will both be nonmetals (or both are from the right hand side of the periodic table). The names of the compounds will include a prefix to indicate the number of atoms of each element. There is no need to balance this type of formula. The second elements name is changed to end in -ide.

Table of Prefixes

one -	mono	six -	hexa
two -	di	seven -	hepta
three -	tri	eight -	octa
four -	tetra	nine -	nona
five -	penta	ten -	deca

An exception to using the prefixes is when the first element has only one atom. The prefix would be mono is not used for this instance. Also determining where the words fit together will take some practice.

Examples:

CO₂	- carbon dioxide
CCl₄	- carbon tetrachloride
S₃N₂	- trisulfur dinitride

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Acids - Acids dissociate into ions when disolved in water. All of the formulas for acids that are dealt with in this section will start with the hydrogen ion. In order to name the compound as an acid, first name the compound as if it were an ionic compound. Use hydrogen as the cation. Then change the name according to the following table.

Table for Naming Acids

Ending of name as an ionic compound	New form of name
-ide	hydro-root-ic acid
-ite	root-ous acid
-ate	root-ic acid

Examples:

Formula	Ionic Name	Acidic Name
HCl	hydrogen chloride	hydrochloric acid
HNO₃	hydrogen nitrate	nitric acid
H₂SO₃	hydrogen sulfite	sulfurous acid

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Practice Click here for practice naming compounds.

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