Nomenclature

Chapter 2

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IUPAC (International Union of Pure and Applied Chemistry; founded 1919), “is the world authority on digital standards in chemistry; chemical nomenclature and terminology, including the naming of new elements in the periodic table; on standardized methods for measurement; and on atomic weights.” IUPAC nomenclature is a method of naming chemical compounds.


Molecular models

Molecules can be represented in various ways.

Name Molecular Formula Structural Formula Konnectivity Formula* Stereochemical Formula

Methane

CH4

CH4

Ethanol

C2H6O

CH3CH2OH

Diethyl ether

C2H6O

CH3OCH3

*See the K? Should be C right? “Connectivity”. So why the K? Because if I put in a C, the code throws an error when building the table. It’s a bug in one of these packages. Not sure which…

Skeletal formulas and molecular models


Click the dropdowns to see the skeletal formulas (line structures) and molecular models for the structures in the table above.

Methane
Ethanol

Dimethyl ether

  • Molecular formulae for compounds consisting of discrete molecules are formulae that describe the composition of the molecule where each element is grouped and the number of each atom of an element type is indicated with a subscript.
  • Structural formulae give information about how certain atoms are grouped together in the molecule.
  • Connectivity formulae give information about the way atoms in a molecule or ion are connected and arranged in space. Lone electron pairs are typically omitted but can be shown as seen here.
  • Stereochemical formulae represents the structure in three dimensions. Lone electron pairs are typically omitted but can be shown as seen here.
  • Molecular models are visualization schemes for visualizing structures in three dimensions. Commonly, ball-and-stick models are used (as seen above in the dropdowns) but a variety of others exist.

Covalent Compounds

Naming covalent (molecular) compounds follow a set of rules that are different than ionic compounds.

Homogeneous polyatomic

Molecules made up of one type of element are called by their element name.

Table 1: Homogeneous polyatomic molecules
Formula Name

H2

hydrogen

N2

nitrogen

O2

oxygen

F2

fluorine

Cl2

chlorine

Br2

bromine

I2

iodine

P4

phosphorous

S8

sulfur

Compounds with common names

Some molecular compounds are well-known by their common names and are not referred to by their IUPAC names.

Table 2: Compounds with common names
Formula Name

H2O

water

H2O2

hydrogen peroxide

NH3

ammonia

N2H4

hydrazine

PH3

phosphine

NO

nitric oxide

N2O

nitrous oxide

CH4

methane

C2H6

ethane

C3H8

propane

Binary Compounds

Most binary compounds are combinations of two nonmetal elements from Groups 14-17 with one another or with hydrogen. Elements are listed in the order of increasing group order. If two elements are in the same group, the element in the largest period is usually written first.

Binary molecular compounds are arranged in the (reverse) order given in Figure 1. That is, the first encountered element is typically preceded by the second encountered element (bottom-left first and top-right last). Hydrogen is a weird exception.

Figure 1: Element sequence as provided by IUPAC5

Hydrogen can form binary compounds with all nonmetals except for the noble gases. Hydrogen is usually written first when in compounds containing oxygen, sulfur, and the halogens. The other nonmetal is named by adding -ide to the stem of the name.

Naming Rules:

  1. The first part of the name is hydrogen if the first element listed is hydrogen
  2. The second part is the root element name followed by -ide
Table 3: Hydrogen binary molecular compound names
Formula Name

HF

hydrogen fluoride

HCl

hydrogen chloride

HI

hydrogen iodide

H2S

hydrogen sulfide

Multiplicative prefixes

Multiplicative prefixes are numerical multipliers in IUPAC nomenclature that indicates the number of particular atoms or functional groups that are in a molecule. These are used when naming most other binary compounds.

Table 4: Multiplicative prexfixes
No. Simple

0.5

hemi

1

mono

2

di

3

tri

4

tetra

5

penta

6

hexa

7

hepta

8

octa

9

nona

10

deca

11

undeca

12

dodeca

Naming binary compounds if molecular:

  1. Element name of nonmetal. Omit “mono” for first element
  2. Root element name of second nonmetal with -ide ending
  3. No prefix if first element is hydrogen
  4. Drop the second “o” in “mono” prior to a vowel
  5. Drop the “a” in prefixes ending in “a” prior to a vowel
Table 5: Binary molecular compound names
Formula Name

CO

carbon monoxide

PBr3

phosphorous tribromide

CCl4

carbon tetrachloride

CS

carbon monosulfide

CaC2

calcium carbide

PI3

phosphorous triiodide

SiS2

silicon disulfide

NCl3

nitrogen trichloride

IF7

iodine heptafluoride

S4N4

tetrasulfur tetranitride

N2O5

dinitrogen pentoxide

I2O5

diiodine pentoxide

Ions

A monatomic ion is a charged particle made up of a single atom. They are named after their element followed by their charge in parenthesis. Monatomic anions are also named after their root element name followed by -ide.

Table 6: Monatomic ion names
Formula Name

H+

hydrogen(1+)
hydron
proton (informally)

Li+

lithium(1+)

Na+

sodium(1+)

K+

potassium(1+)

Mg2+

magnesium(2+)

Ca2+

calcium(2+)

Al3+

aluminum(3+)

Co2+

cobalt(2+)

Fe3+

iron(3+)

Sc4+

scandium(4+)

H

hydrogen(1–)
hydride

S2–

sulfur(2–)
sulfide

N3–

nitrogen(3–)
nitride

F

fluoride(1–)
fluoride

Cl

chloride(1–)
chloride

Br

bromide(1–)
bromide

I

iodide(1–)
iodide

Figure 2 shows the typical charge(s) some elements adopt when becoming an ion.

Figure 2: Typical charges of monatomic ions

The following transition metals are said to be (for this class) invariant, that is, they only adopt one charge.

  • Cd2+
  • Zn2+
  • Ag+

Polyatomic ions

A polyatomic ion is a molecular ion with a non-zero charge containing two or more covalently bound atoms or of a metal complex, that can behave as a single unit (Table 7).

Table 7: Examples of polyatomic ions
Formula Name
Anions: Group 12

Hg22+

mercury(I) ion

Cations: Group 15

NH4+

ammonium ion

Cations: Group 16

H3O+

hydronium ion

Anions: Group 14

CN

cyanide ion

CH3CO2
CH3COO

acetate ion

CO32–

carbonate ion

HCO3

hydrogen carbonate ion

HCOO
HCO2

formate ion

C2H5O

ethoxide ion

C2O42–

oxalate ion

Anions: Group 15

NO2

nitrite ion

NO3

nitrate ion

PO43–

phosphate ion

HPO42–

hydrogen phosphate ion

H2PO4

dihydrogen phosphate ion

Anions: Group 16

O22–

peroxide ion

OH

hydroxide ion

SO32–

sulfite ion

SO42–

sulfate ion

Transition metals

CrO42–

chromate ion

Cr2O72–

dichromate ion

MnO4

permanganate ion

Oxyanions

Most polyatomic ions are oxyanions (or oxoanions), conjugate bases of oxyacids. For example, the phosphate anion, PO43–, is an oxyanion that is a conjugate base of the parent H3PO4 molecule (phoshporic acid). The suffixes ‘-ide’, ‘-ite’, ‘-ate’, and prefixes ‘hypo-’ and ‘per-’ are used in a systematic fashion depending on the number of oxygen atoms present.

The order of these pre/suffixes from least to most oxygens present is as follows:

hypo…ite → …ite → …ate → per…ate


Table 8 illustrate these naming schemes.

Table 8: Examples of oxyanions
Formula Name
Anions: Group 15

NO2

nitrite ion

NO3

nitrate ion

PO33–

phosphite ion

PO43–

phosphate ion

PO53–

perphosphate ion

Anions: Group 16

SO32–

sulfite ion

SO42–

sulfate ion

Anions: Group 17

ClO

hypochlorite ion

ClO2

chlorite ion

ClO3

chlorate ion

ClO4

perchlorate ion

BrO

hypobromite ion

BrO2

bromite ion

BrO3

bromate ion

BrO4

perbromate ion

IO

hypoiodite ion

IO2

iodite ion

IO3

iodate ion

IO4

periodate ion

Binary Ionic Compounds

Ionic compounds form between cations and anions about an ionic bond. Naming ionic compounds depend on the types of charged particles in the compound. These particles can be

  • Metals of one charge (invariant)
    • non-transition metals
    • Cd, Ag, Zn (treated as invariant for this class)
  • Metals that can adopt various charges (multivalent)
    • most transition metals
  • Non-metals
  • Polyatomic Ions

The charge of the multivalent metal can be deduced by considering the charge of the other particle and the charge on the overall compound. For example, the charge on iron in FeCl2 is 2+ because each chlorine atom adopts a 1– charge giving a neutral ionic compound.

Invariant metal + nonmetal

Naming rules:

  1. Elemental name of metal
  2. Elemental root name of nonmetal with “ide” ending

Remember that Cd, Zn, and Ag are considered to be invariant (for this class) and adopt the following charges:

  • Cd2+
  • Zn2+
  • Ag+
Table 9: Ionic compounds: invariant metal + nonmetal
Formula Name

NaCl

sodium chloride

KBr

potassium bromide

MgCl2

magnesium chloride

CaBr2

calcium bromide

Al2O3

aluminum oxide

CdBr2

cadmium bromide

AgCl2

silver chloride

ZnCl

zinc chloride

Invariant metal + polyatomic ion

Naming rules:

  1. Elemental name of metal
  2. Name of polyatomic ion (see Table 7)
Table 10: Ionic compounds: invariant metal + polyatomic ion
Formula Name

Ca3(PO4)2

calcium phosphate

MgCO3

magnesium carbonate

NaNO3

sodium nitrate

MgSO4

magnesium sulfate

NaOH

sodium hydroxide

Multivalent metal + nonmetal

Naming rules:

  1. Elemental name of transition metal
  2. Use Roman numerals in parenthesis immediately following transition metal name (no space) to define the oxidation state (which is equal to the charge on the metal)
  3. Elemental root name of nonmetal with “ide” ending
Table 11: Ionic compounds: multivalent metal + nonmetal
Formula Name

FeCl2

iron(II) chloride

FeCl3

iron(III) chloride

FeCl3

iron(III) chloride

Co2O3

colbalt(III) oxide

CoCl2

cobalt(II) chloride

Multivalent metal + polyatomic ion

Naming rules:

  1. Elemental name of metal
  2. Use Roman numerals in parenthesis immediately following transition metal name (no space) to define the oxidation state (which is equal to the charge on the metal)
  3. Name of polyatomic ion (see Table 7)
Table 12: Ionic compounds: multivalent metal + polyatomic ion
Formula Name

Fe(NO3)3

iron(III) nitrate

CuSO4

copper(II) sulfate

Mn2O4

manganese(II) permanganate

CoCO3

cobalt(II) carbonate

Ni(OH)2

nickel(II) hydroxide

Polyatomic ion + nonmetal

Naming rules:

  1. Name the element or polyatomic ion (whichever comes first)
  2. Name the element or polyatomic ion (whichever comes second). If the second particle is an element, write out the root name of the element and end it with -ide.
Table 13: Ionic compounds: polyatomic ion + nonmetal
Formula Name

NaOH

sodium hydroxide

CaCO3

calcium carbonate

NH4Cl

ammonium chloride

(NH4)2O

ammonium oxide

Polyatomic ion + polyatomic ion

Naming rules:

  1. Name the first polyatomic ion
  2. Name the second polyatomic ion
Table 14: Ionic compounds: polyatomic ion + polyatomic ion
Formula Element

(NH4)2CO3

ammonium carbonate

(NH4)2SO4

ammonium sulfate

Hydrates

Hydrates are substances that contain water. Hydrated ionic compounds are ionic compounds that contain water. If hydrate ionic compounds are dried, they are referred to as being anhydrous.

Naming rules:

  1. Name the ionic compound first following the rules for naming ionic compounds
  2. Name the number of waters by using the appropriate multiplicative prefix (Table 4) conjoined with the word “hydrate”

Note that chemical formulas for hydrates contain a center/middle dot that separate the compound from the waters.

Table 15: Ionic compounds: hydrates
Formula Name

CaSO4 · 0.5 H2O

calcium sulfate hemihydrate

Ba(OH)2 · 8 H2O

barium hydroxide octahydrate

CoCl2 · 6 H2O

cobalt(II) chloride hexahydrate

FeCl2 · 4 H2O

iron(II) chlroide tetrahydrate

FeCl3 · 6 H2O

iron(III) chloride hexahydrate

Simple Organic Compounds

Organic compounds are defined in a couple different of ways:

  • compounds that contain a carbon-hydrogen or carbon-carbon (e.g. CH4)
  • any chemical compound that contains carbon (e.g. CCl4, CN, HCN, and CO2)

Hydrocarbons are molecules consisting of only carbon and hydrogen.

Alkanes

Alkanes are acyclic saturated hydrocarbons (each carbon forms four single bonds with other carbon or hydrogen atoms). Alkanes can exist as structural isomers, more than one compound with the same chemical formula but existing with a different arrangement of bonds.

Structural Isomers of C5H12


Pentane

Isopentane

Neopentane

Prefixes are used depending on the number of carbon atoms present (Table 16).

Table 16: Some prefixes used in the naming of organic compounds
Number of carbons Prefix

1

meth

2

eth

3

prop

4

but

5

pent

6

hex

7

hept

8

oct

9

non

10

dec

11

undec

12

dodec

Alkanes containing a single chain of saturated carbon atoms (where each carbon forms four single bonds) without any branching (referred to as linear) are named by first using the appropriate prefix followed by “ane”. Sometimes, ‘n-’ (for normal) is included at the front of the name for these molecules but can be omitted.

Table 17: Examples of linear alkanes
Number of Carbons Formula Name

1

CH4

methane

2

C2H6

ethane

3

C3H8

propane

4

C4H10

butane

5

C5H12

pentane

6

C6H14

hexane

7

C7H16

heptane

8

C8H18

octane

9

C9H20

nonane

10

C10H22

decane

11

C11H24

undecane

12

C12H26

dodecane

Alcohols

Alcohols are organic compounds that contain at least one hydroxyl (–OH) functional group. The simplest alcohols are similar to alkanes in structure and in naming. Use the appropriate prefix (Table 16) associated with the number of carbon atoms followed by “anol” as the suffix. The leading “1-” can be excluded.

Table 18: Examples of linear alcohols
Numbe of Carbons Formula Condensed Formula IUPAC Name

1

CH4O

CH3OH

methanol

2

C2H6O

C2H5OH

ethanol

3

C3H8O

C3H7OH

propanol

4

C4H10O

C4H9OH

butanol

5

C5H12O

C5H11OH

pentanol

6

C6H14O

C6H13OH

hexanol

7

C7H16O

C7H15OH

heptanol

8

C8H18O

C8H17OH

octanol

9

C9H20O

C9H19OH

nonanol

10

C10H22O

C10H21OH

decanol

11

C11H24O

C11H23OH

undecanol

12

C12H26O

C12H25OH

dodecanol

Carboxylic acids

Carboxylic acids are organic compounds that contain at a carboxyl group (–COOH or –C(=O)–OH) functional group. Naming of straight chain carboxylic acids is similar to naming alkanes. Use the appropriate prefix (Table 16) associated with the number of carbon atoms followed by “anoic” as the suffix and terminate the name with the word “acid”.

Table 19: Examples of carboxylic acids
Number of Carbons Formula Condensed Formula Name

1

CH2O2

HCOOH

methanoic acid

2

C2H4O2

CH3COOH

ethanoic acid

3

C3H6O2

CH3CH2COOH

propanoic acid

4

C4H8O2

CH3CH2CH2COOH

butanoic acid

5

C5H10O2

CH3(CH2)3COOH

pentanoic acid

6

C6H12O2

CH3(CH2)4COOH

hexanoic acid

7

C7H14O2

CH3(CH2)5COOH

heptanoic acid

8

C8H16O2

CH3(CH2)6COOH

octanoic acid

9

C9H18O2

CH3(CH2)7COOH

nonanoic acid

10

C10H20O2

CH3(CH2)8COOH

decanoic acid

11

C11H22O2

CH3(CH2)9COOH

undecanoic acid

12

C12H24O2

CH3(CH2)10COOH

dodecanoic acid

Acids and Bases

Below is a table of common strong and weak acids and bases. Note that many acids exist naturally as a gas (e.g. HCl(g) is hydrogen chloride). Sometimes, if the substance is dissolved in a solvent (such as water), and meets the definition of an acid, only then is it called an acid (e.g. HCl(aq) is hydrochloric acid). Exceptions include organic compounds such as carboxylic acids (e.g. acetic acid) which are still referred to as their acid name even in the absence of water. Anhydrous acetic acid is also called “glacial acetic acid”.

Table 20: Common strong and weak acids and bases
Formula Name
Strong Acid

HCl(aq)

hydrochloric acid

HBr(aq)

hydrobromic acid

HI(aq)

hydroiodic acid

HNO3(aq)

nitric acid

HClO3(aq)

chloric acid

HClO4(aq)

perchloric acid

H2SO4(aq)

sulfuric acid

Weak Acid

HF(aq)

hydrofluoric acid

H3PO4(aq)

phosphoric acid

H2CO3(aq)

carbonic acid

CH3CO2H(aq)

acetic acid

H2C2O4(aq)

oxalic acid

H2C4H4O6(aq)

tartaric acid

H3C6H5O7(aq)

citric acid

HC9H7O4(aq)

aspirin

Strong Base

LiOH

lithium hydroxide

NaOH

sodium hydroxide

KOH

potassium hydroxide

Ba(OH)2

barium hydroxide

Ca(OH)2

calcium hydroxide

Sr(OH)2

strontium hydroxide

Weak Base

NH3

ammonia

References

(1)
Leigh, G. J. Principles of Chemical Nomenclature: A Guide to IUPAC Recommendations; EBL-schweitzer; Royal Society of Chemistry, 2011.
(2)
Connelly, N. G.; Chemistry (Great Britain), R. S. of; Pure, I. U. of; Chemistry, A. Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005; Royal Society of Chemistry, 2005.
(3)
Favre, H. A.; Powell, W. H. Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013; International union of pure and applied chemistry; Royal Society of Chemistry, 2014.
(4)
Jones, R. G.; Wilks, E. S.; Metanomski, W. V.; Kahovec, J.; Hess, M.; Stepto, R.; Kitayama, T. Compendium of Polymer Terminology and Nomenclature: IUPAC Recommendations 2008; Royal Society of Chemistry, 2009.
(5)
Hartshorn, R. M.; Hellwich, K.-H.; Yerin, A.; Damhus, T.; Hutton, A. T. Brief Guide to the Nomenclature of Inorganic Chemistry. Pure and Applied Chemistry 2015, 87 (9-10), 1039–1049. https://doi.org/doi:10.1515/pac-2014-0718.