Chem Professor

Tutorial

04/25/09

Inorganic Nomenclature, Text Version

�Before You Begin:

This tutorial is a short summary of the rules of nomenclature and practice problems. Before you begin, review the types of compounds and the periodic table.

Naming Common Compounds

Classifying Inorganic Compounds

There are three types of common inorganic compounds. They are

l   Ionic compounds

l   Molecular compounds

l   Acids

Compounds not covered in this tutorial include:

l Organic compounds

l Organic compounds contain carbon. To identify organic compounds look for carbon (except for carbon dioxide, carbon monoxide, and carbonate ion, which are considered to be inorganic).

l Coordination compounds

l Coordination compounds have special bonds in which molecules and ions donate pairs of electrons to metal cations. These compounds look like ionic compounds but have complex ions written in square brackets. To identify coordination compounds look for [ ].

Ionic Compounds

l Ionic compounds are composed of positively and negatively charged ions and are held together by electrostatic attractions called ionic bonds.

l Ionic compounds do not contain molecules.

Identifying Ionic Compounds

l Metals tend to form positive ions, and non-metals tend to form negative ions.

l Hydrogen, H⁺¹, and ammonium ion, NH₄⁺¹, are the only common positive ions that do not contain a metal.

l Of these two, ammonium is found in ionic compounds, and hydrogen is found in acids.

l To identify a compound as being ionic, scan the name or the formula and identify the elements.

l If the compound contains a metal (or the ammonium ion) and at least one non-metal, it is almost always an ionic compound.

Naming Ionic Compounds

l Ionic compound names have two parts: the cation (positive ion) name and the anion (negative ion) name.

l The positive ion is written first. Example: K₂S is potassium sulfide. Potassium is the name of the cation; sulfide is the name of the anion.

l Cations have the same name as their element, though they may also have a number. Example: Mg⁺² is the magnesium ion; Fe⁺³ is the iron (III) ion.

l Anions with only one atom have the same root name as their element but end with the suffix “-ide.” Example: Cl^-1 is the chloride ion.

l You will need to learn the names of the monatomic (single atom) ions and their charges. This is a periodic property.

l Many metals can form more than one cation. These metals can be found in the transition and lower p-block parts of the periodic table.

l The names of these ions have Roman Numerals in parenthesis after the metal name. This number is the charge of the ion. Example: FeCl₃ is iron (III) chloride, because the iron ion in this compound has a +3 charge. FeCl₂ is iron (II) chloride, because the iron ion has a +2 charge.

Common Monatomic Ions and Their Charges
Periodic Table Group/Region	Ion Charge	Notes
Group 1, Alkali metals	+1 only	Roman numerals not needed. H is the exception. It can have a +1 charge (as an acid) or a -1 charge (as a hydride with a metal).
Group 2, Alkaline Earth	+2 only	Roman numerals not needed.
Group 17, Halogens	-1 in ionic compounds
Group 16	-2 charge when monatomic	Sulfur and oxygen can form polyatomic ions that can be misleading. Peroxide ion is O₂-², for example.
Transition metals	Variable, many transition metals have more than one possible charge.	Use Roman numerals. The exceptions are Ag⁺¹, Zn⁺², and Cd⁺². These don’t form other ions and don’t need Roman numerals.
p-Block Metals	Variable, many have more than one possible charge. Some of the semi-metals can form positive or negative ions.	Use Roman numerals. The exceptions are Al⁺³ and Po⁺².

l Many ionic compounds have polyatomic (many atom) ions.

l To name these, name the cation then the anion. Example: NH₄OH is ammonium hydroxide.

l In order to name ionic compounds (and acids) you will need to memorize the names of the common polyatomic ions.

Common Polyatomic IOns and Their Charges
Charge	Formula	Name
+1	NH₄⁺¹	Ammonium
+2	Hg₂⁺²	Mercury (I)
-1	CN^-1 OH^-1 C₂H₃O₂^-1 NO₃^-1 NO₂^-1 MnO₄^-1 ClO^-1 ClO₂^-1 ClO₃^-1 ClO₄^-1 HCO₃^-1 H₂PO₄^-1	Cyanide Hydroxide Acetate Nitrate Nitrite Permanganate Hypochlorite Chlorite Chlorate Perchlorate Hydrogen carbonate Dihydrogen phosphate
-2	CO₃^-2 CrO₄^-2 Cr₂O₇^-2 SO₄^-2 SO₃^-2 HPO₄^-2	Carbonate Chromate Dichromate Sulfate Sulfite Hydrogen phosphate
-3	PO₄^-3	Phosphate

Name these ionic compounds:

Zn₃(PO₄)₂

CuCl₂

NH₄NO₃

Cu₂S

KC₂H₃O₂

(NH₄)₂Cr₂O₇

Answers

Zn₃(PO₄)₂is zinc phosphate.

CuCl₂ is copper (II) chloride.

NH₄NO₃ is ammonium nitrate.

Cu₂S is copper (I) sulfide.

KC₂H₃O₂ is potassium acetate.

(NH₄)₂Cr₂O₇is ammonium dichromate.

Formulas of Ionic Compounds

l If given the name, identify the formulas of each of the ions then use subscripts to make the charges neutral.

Examples:

Magnesium bromide contains the ions Mg⁺² and Br ^-1, so the formula is MgBr₂.

Tin (IV) sulfate contains the ions Sn⁺⁴ and SO₄^-2, so the formula is Sn(SO₄)₂.

Write the formula for these compounds:

Ammonium sulfite

Magnesium hydrogen carbonate

Iron (III) oxide

Answers

Ammonium sulfite is (NH₄)₂SO₃.

Magnesium hydrogen carbonate is Mg(HCO₃)₂.

Iron (III) oxide is Fe₂O₃.

Acids

l Acids are substances that react with water to form an aqueous hydrogen ion, H⁺¹(aq).

l These compounds have characteristics in common with both ionic and molecular compounds.

Identifying Acids

l There are different systems for classifying acids. Some acids have names that fit the following rules. Others have names that fit the ionic or binary molecular compound naming rules.

l To determine if a compound is an acid for naming purposes, scan the chemical formula. The formula for an acid begins with H.

Naming Acids

l Scan the formula. Identify the anion. Acid names use the name of the anion as a root word for the acid name. Example: HF is hydrofluoric acid. It has a root word “fluor-” from the name of the fluoride ion.

l If the name of the anion ends with the suffix “-ate” the acid name will have the format “___ic acid.” Example: H₂SO₄ is sulfuric acid because SO₄^-2 is the sulfate ion.

l If the name of the anion ends in with the suffix “_ite” the acid name will have the format “___ous acid.” Example: HNO₂ is nitrous acid because NO₂^-1 is the nitrite ion.

l If the name of the anion ends with the suffix “-ide” the acid name will have the format “hydro___ic acid.” Example: HCN is hydrocyanic acid because CN^-1 is the cyanide ion.

Name the following acids:

HCl

H₂CrO₄

HClO

Answers

HCl is hydrochloric acid.

H₂CrO₄ is chromic acid.

HClO is hypochlorous acid.

Formulas of Acids

l To write the formula from the name, use the format and root to identify the anion. Write H¹⁺ and the anion and use subscripts to make the compound neutral.

l Phosphoric acid has the “___ic acid” format, so the anion name ends in “-ate” and contains phosphorus. The anion is phosphate ion, PO₄^-3. The acid must be H₃PO₄.

Give the formulas of these acids:

Hydroselenic acid

Perchloric acid

Sulfurous acid

Answers

Hydroselenic acid is H₂Se.

Perchloric acid is HClO₄.

Sulfurous acid is H₂SO₃.

Molecular Compounds

Molecular compounds are composed of molecules in which atoms share electrons via bonds.

Identifying Molecular Compounds

l Molecular compounds contain two or more non-metals but not the ammonium ion, NH₄⁺¹.

l To determine if a compound is molecular scan the formula for a metal or the ammonium ion—these will be written at the beginning of the formula. If the compound does not contain a metal, it is probably molecular.

l Compound that have formulas beginning with H and anion with names ending in “-ide” can be named as acids or molecular compounds.

l If the compound is in aqueous solution, name it as an acid. Example: HF_(aq) is hydrofluoric acid.

l If the compound is a gas, name it as a molecular compound. Example: H₂S_(g)is hydrogen sulfide.

l Organic compounds contain carbon. Some organic compounds follow the general rules for binary molecular compounds (carbon dioxide, carbon monoxide, carbon tetrachloride) but most follow a special naming system.

Binary Molecular Compounds

l Binary molecular compounds contain two non-metals.

l Some have common names from antiquity. Common names you will need to know: ammonia, NH₃, and water, H₂O.

Naming Binary Molecular Compounds

l The first element in the formula is the first element in the name. Example: CO₂ is carbon dioxide; the same order in the name as in the formula.

l Use prefixes to indicate the number of atoms of each of the elements in the molecule. Example: CO₂ is carbon dioxide; di- prefix for two oxygen atoms.

Binary Molecular Compound Prefixes
Number	Prefix	Number	Prefix
1	Mono-	6	Hexa-
2	Di-	7	Hepta-
3	Tri-	8	Octa-
4	Tetra-	9	Nona-
5	Penta-	10	Deca-

l The two elements in the compound are named as two separate words. Each word will have its own prefix. The prefix “mono-” is not used for the first element. Example: CO₂ is carbon dioxide NOT monocarbon dioxide.

l End the name with the suffix “-ide.” Example: CO₂ is carbon dioxide; the name ends with “-ide.”

l More Examples

SF₆ is sulfur hexafluoride.

N₂O₅ is dinitrogen pentoxide.

Cl₂O is dichlorine monoxide.

Note that an extra vowel was dropped in the names of the last two. This makes the names easier to pronounce.

Name the following compounds:

l XeF₆

l I₂O₄

l SO₃

Answer

l XeF₆is xenon hexafluoride.

l I₂O₄ is diiodine tetroxide.

l SO₃ is sulfur trioxide.

Formulas of Binary Molecular Compounds

l To write the formula from the name of a binary molecular compound, scan the name and identify the two non-metallic elements.

l Write the symbol for the first element first and the second element second.

l Use the numbers from the prefixes as subscripts.

Example:

Tetraphosphorus decasulfide has P and S as the elements in its formula.

P will appear first in the formula.

The subscript on P is 4. The subscript on S is 10.

The formula is P₄S₁₀.

Give the formulas of the following binary molecular compounds:

Xenon dioxide

Dinitrogen tetrachloride

Answer

Xenon dioxide is XeO₂.

Dinitrogen tetrachloride is N₂Cl₄.

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