101Nomenclature

Chemical Nomenclature

Chemical nomenclature refers to a systematic method of naming chemical compounds. Chemical nomenclature is a major portion of the language of chemistry. If you are able to write the formula for a compound, you will be able to predict its name and vice versa. We have two methods of naming compounds, the systematic method or the common name. The systematic method comes from the IUPAC (International Union of Pure and Applied Chemistry), a system developed in 1921 by a group made up of chemists from all over the world. This system has specific rules and has developed an unambiguous method of naming compounds. There are no rules for the common names (H₂O is water, for example).

Goals:

Write the name and formula of binary compounds made from 2 nonmetals.

Use the periodic table to predict the charge for an atom.

Write the correct formula for a binary ionic compound

Write the correct formula for an ionic compound that contains a polyatomic ion.

Correctly name an ionic compound.

Binary compounds made from nonmetals.

The formula of a binary compound make only from nonmetals can easily be deduced from its name. The name of the compound contains the name of both elements. The name of the second elements ends in "ide". For example, CO is called carbon monoxide. A prefix is used to indicate the number of each element in the compound.

Greek prefixes
Mono-	One
Di-	Two
Tri-	Three
Tetra-	Four
Penta-	Five
Hexa-	six

If there is only one of the first element in the compound, the mono is left off. Hence, CO Examples:

1. CO is made from one carbon atom and one oxygen atom and is called carbon monoxide.
2. CO₂ is made from one carbon and two oxygens and is called carbon dioxide.
3. N₂O₄ is made from two nitrogens and two oxygens and is called dinitrogen tetroxide.

Binary ionic compounds

Binary ionic compounds have a completely different set of rules and it is imperative that the rules are not confused. A binary ionic compound contains only a single type of each of a metal and a nonmetal. When the formula for an ionic compound is written, the cation is written first followed by the anion. When an ionic compound is named the cation is also named first. The cation is named for the metallic element from which it is obtained. The anion is written and named second. Monatomic anions are named from the root name of the element followed by "-ide". For example: NaCl is named sodium chloride.

We can frequently determine the charge on the ions just from their location on the periodic table.

The elements from Group I have one electron in their outer shell and always ionize to a charge of +1. The elements from Group VII (7) have 7 electrons in their outer shell and gain one electron when they form ions. Many of the metals have more that one possible charge. These elements are named differently. For example: Iron forms both a Fe²⁺ and Fe³⁺ ion. To distinguish between these two ions we use the Stock system. In the Stock system, the charge for cation is written in Roman numerals and put in parenthesis immediately following the name of the cation. Fe³⁺ is iron (III). Pb⁴⁺ is lead (IV).

Group I Group II Group III Group V Group VI GroupVII

Li⁺ Be²⁺ N^3— O^2— F^—

Na⁺ Mg²⁺ Al³⁺ P^3— S^2— Cl^—

K⁺ Ca²⁺ Se^2— Br^—

Rb⁺ Sr²⁺ I^—

Cs⁺ Ba²⁺

From Various groups:

Zn²⁺

Cd²⁺

Ag⁺

Some common metals with more than one possible charge:

Fe²⁺ iron (II) or Fe³⁺ iron (III)

Co²⁺ cobalt (II) or Co³⁺ cobalt (III)

Cu⁺ copper (I) or Cu²⁺ copper (II)

Sn²⁺ tin (II) or Sn⁴⁺ tin (IV)

Pb²⁺ lead (II) or Pb⁴⁺ lead (IV)

Cr²⁺ chromium (II) or Cr³⁺ chromium (III)

Mn²⁺ manganese (II) or Mn⁴⁺ manganese (IV)

Hg₂²⁺ mercury (I) or Hg²⁺ mercury (II)

Ionic compounds are electrically neutral. That is, they have the same number of positive and negative charges.

1. Since sodium is Na⁺ and chloride is Cl^—, the formula is NaCl and the name is sodium chloride.
2. Calcium oxide is formed from Ca²⁺ and O^2— and the formula is CaO.
3. Magnesium bromide is formed from Mg²⁺ and Br^—. There must be two Br^— for every Mg. The formula is MgBr₂.
4. Tin (IV) sulfide is made from Sn⁴⁺ and S^2—. There must two S^2— for every Sn⁴⁺. The formula is SnBr₂.

Ternary or Higher Compounds

Compounds containing three or more elements (usually in the form of polyatomic ions) are very common and follow the same system. The only complication is that the formula charge and name of the polyatomic ion to determine the formula of the compound. This information must be memorized. There is only one common polyatomic cation, ammonium, NH₄⁺. Many of the polyatomic anions contain oxygen with another element. These oxyanions are named from their nonoxygen element with usually either and "-ite" or "-ate" ending. This ending gives an indication of how much oxygen is present in the ion. This list of polyatomic anions must be memorized.

- 1 charge		-1 charge
nitrite	NO₂^—	permanganate	MnO₄^—
nitrate	NO₃^—	acetate	C₂H₃O₂^—
hypochlorite	ClO^—	hydroxide	OH^—
chlorite	ClO₂^—	hydrogen sulfite	HSO₃^—
chlorate	ClO₃^—	hydrogen sulfate	HSO₄^—
perchlorate	ClO₄^—	hydrogen carbonate	HCO₃^—
cyanide	CN^—

-2 charge		-3 charge
sulfite	SO₃^2—	phosphate	PO₄^3—
carbonate	CO₃^2—
sulfate	SO₄^2—
chromate	CrO₄^2—
dichromate	Cr₂O₇^2—
oxalate	C₂O₄^2—

The best way to understand the polyatomic anions is to draw Lewis Structures for them. The rules for writing the formulas for Ternary and higher compounds are similar to binary ionic compounds.

1. Barium sulfate is Ba²⁺ with SO₄^2— . There will be one barium atom per sulfate and the formula is BaSO₄.
2. Calcium hydroxide is Ca²⁺ with OH^—. There will be two hydroxides with one calcium atom. The formula is Ca(OH)₂. To make sure that we have two OH^— we must use parenthesis around the OH^—. If we wrote the formula without ( ), it would be CaOH₂. This is 1 Ca, 1 O and 2 H. This does not give us 2 OH^—.
3. Iron (III) oxalate. This is Fe³⁺ with C₂O₄^2—. To balance the charges, we must have 2 Fe³⁺ with 3 C₂O₄^2—. The formula would be Fe₂(C₂O₄)₃.

Likewise we can go from the formula to the name.
1. AgNO₃ is Ag⁺ with NO₃^—. The name is silver nitrate.
2. CrPO₄ is Cr³⁺ with PO₄^3—. We know that the charge on the chromium must be +3 since chromium is 1:1 with phosphate and the charge on phosphate is –3. The name is chromium (III) phosphate.
3. Hg₂Cl₂ is Hg₂²⁺ with 2 Cl^—. Hg₂²⁺ is mercury (I) and the name is mercury (I) chloride.

Group I	Group II	Group III	Group V	Group VI	GroupVII
Li⁺	Be²⁺		N^3—	O^2—	F^—
Na⁺	Mg²⁺	Al³⁺	P^3—	S^2—	Cl^—
K⁺	Ca²⁺			Se^2—	Br^—
Rb⁺	Sr²⁺				I^—
Cs⁺	Ba²⁺