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Comprehensive Study Guide: Chemical Nomenclature in General Chemistry

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Chemical Nomenclature

Introduction to Nomenclature

Chemical nomenclature is the systematic method used to name chemical compounds and write their formulas. Mastery of nomenclature is essential for clear communication in chemistry, allowing chemists to identify, discuss, and analyze substances efficiently. The rules differ for various classes of compounds, including ionic, covalent, acids, hydrates, and simple organic molecules.

  • Key Point 1: Nomenclature distinguishes between organic and inorganic compounds. Organic compounds contain carbon; inorganic compounds generally do not.

  • Key Point 2: Inorganic compounds are further classified as ionic or covalent.

  • Example: NaCl is named sodium chloride, following ionic compound rules.

Binary Ionic Compounds

Formation and Naming Rules

Binary ionic compounds consist of a metal cation and a nonmetal anion, held together by electrostatic forces. The charge of ions is often predictable based on their group in the periodic table.

  • Key Point 1: The compound must be electrically neutral.

  • Key Point 2: The cation is named first, followed by the anion with the suffix "-ide".

  • Key Point 3: Transition metals may have multiple charge states; their charge is indicated by Roman numerals in parentheses (systematic/IUPAC) or by suffixes "-ic" (higher charge) and "-ous" (lower charge) in non-systematic names.

  • Example: FeCl3 is iron(III) chloride or ferric chloride.

Group Trends for Ion Formation

Group

Trend

Notes

1A

+1 cations

2A

+2 cations

3A

+3 cations

Only Al; others variable

4A

No overall trend

Mix of metals/nonmetals

5A

-3 anions

Only N; others variable

6A

-2 anions

O, S, Se

7A

-1 anions

8A

Does not form ions

Noble gases

Nomenclature for Cations with Multiple Charges

Cation

Systematic Name

Non-systematic Name

Fe2+

iron(II)

ferrous

Fe3+

iron(III)

ferric

Co2+

cobalt(II)

cobaltous

Co3+

cobalt(III)

cobaltic

Cu+

copper(I)

cuprous

Cu2+

copper(II)

cupric

Sn2+

tin(II)

stannous

Sn4+

tin(IV)

stannic

Hg+ (Hg22+)

mercury(I)

mercurous

Hg2+

mercury(II)

mercuric

Pb2+

lead(II)

plumbous

Pb4+

lead(IV)

plumbic

Hydrates and Polyatomic Ions

Hydrates

Hydrates are ionic compounds with a specific number of water molecules attached to each formula unit. The number of water molecules is indicated by a numerical prefix.

  • Key Point 1: The compound's name is followed by "hydrate" with a prefix indicating the number of water molecules.

  • Example: MgCl2·2H2O is magnesium chloride dihydrate.

Numerical Prefixes for Hydrates and Covalent Compounds

Number

Prefix

1

mono-

2

di-

3

tri-

4

tetra-

5

penta-

6

hexa-

7

hepta-

8

octa-

9

nona-

10

deca-

Polyatomic Ions

Polyatomic ions are groups of covalently bonded atoms carrying a net charge. Most are anions, but some cations exist.

  • Key Point 1: Polyatomic ions remain intact as a unit in compounds.

  • Key Point 2: Oxoanions (contain oxygen) follow naming rules based on the number of oxygen atoms.

  • Example: NO3- is nitrate; NO2- is nitrite.

Rules for Oxoanions

  • For families with two members:

    • More O atoms: root + "-ate"

    • Fewer O atoms: root + "-ite"

  • For families with four members:

    • Most O atoms: "per-" + root + "-ate"

    • 1 fewer O atom: root + "-ate"

    • 2 fewer O atoms: root + "-ite"

    • Fewest O atoms: "hypo-" + root + "-ite"

Common Polyatomic Ions

Ion

Name

Ion

Name

NO2-

Nitrite

CO32-

Carbonate

NO3-

Nitrate

HCO3-

Hydrogen carbonate (bicarbonate)

OH-

Hydroxide

CN-

Cyanide

SO32-

Sulfite

PO43-

Phosphate

SO42-

Sulfate

HPO42-

Hydrogen phosphate

HSO4-

Hydrogen sulfate

H2PO4-

Dihydrogen phosphate

CH3COO-

Acetate

ClO4-

Perchlorate

CrO42-

Chromate

ClO3-

Chlorate

Cr2O72-

Dichromate

ClO2-

Chlorite

MnO4-

Permanganate

ClO-

Hypochlorite

O22-

Peroxide

SCN-

Thiocyanate

BrO3-

Bromate

S2O32-

Thiosulfate

NH4+

Ammonium

Acids

Classification and Naming

Acids are compounds in which hydrogen atoms balance the negative charge of anions. They are classified as binary acids (no oxygen) or oxoacids (contain oxygen).

  • Key Point 1: Binary acids use the prefix "hydro-" and suffix "-ic" followed by "acid".

  • Key Point 2: Oxoacids are named based on the oxoanion: "-ate" becomes "-ic acid", "-ite" becomes "-ous acid"; prefixes are retained.

  • Example: HCl (aq) is hydrochloric acid; H2SO4 is sulfuric acid.

Binary Covalent Compounds

Naming Rules

Binary covalent compounds consist of two nonmetals. The naming system uses prefixes to indicate the number of atoms and the suffix "-ide" for the second element.

  • Key Point 1: The more metallic element (leftmost/lower on the periodic table) is named first.

  • Key Point 2: The second element uses its root name plus "-ide".

  • Key Point 3: Numerical prefixes indicate the number of atoms; "mono-" is omitted for the first element.

  • Example: N2O5 is dinitrogen pentoxide.

Simple Organic Compounds: Alkanes

Straight Chain Alkanes

Alkanes are hydrocarbons containing only carbon and hydrogen, with the formula CnH2n+2 for straight chains. The name is based on the number of carbon atoms, using specific prefixes.

  • Key Point 1: The suffix "-ane" is used for all alkanes.

  • Key Point 2: The prefix indicates the number of carbons.

  • Example: C3H8 is propane.

Organic Nomenclature of Straight Chain Alkanes

Number of Carbons

Prefix

1

meth-

2

eth-

3

prop-

4

but-

5

pent-

6

hex-

7

hept-

8

oct-

9

non-

10

dec-

Summary Table: Nomenclature Types and Examples

Compound Type

Naming Rule

Example

Binary Ionic

Cation + Anion(-ide)

NaCl: sodium chloride

Transition Metal Ionic

Cation (Roman numeral) + Anion(-ide)

FeCl3: iron(III) chloride

Hydrate

Ionic name + prefix + hydrate

CuSO4·5H2O: copper(II) sulfate pentahydrate

Polyatomic Ionic

Cation + Polyatomic Anion

NaNO3: sodium nitrate

Binary Acid

hydro- + root + -ic acid

HCl (aq): hydrochloric acid

Oxoacid

Oxoanion name (-ate/-ite) + -ic/-ous acid

H2SO4: sulfuric acid

Binary Covalent

Prefix + element + prefix + root + -ide

CO2: carbon dioxide

Alkane

Prefix (number of C) + -ane

C4H10: butane

Additional info:

  • For polyatomic ions, memorization is often required, but patterns in naming can help predict names.

  • Some compounds have common or historical names that differ from systematic nomenclature.

  • Organic nomenclature becomes more complex with branching or functional groups, which are not covered here.

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