Nomenclature

Chapter 2

Audio Summary

Audio created by Google NotebookLM. Note: I have not verified the accuracy of the audio or transcript. Download the transcript here (created by Restream).


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.

Element atomic symbols

Element atomic symbols consist of one, two, or three roman letters. Heavier elements that do not have an official name or have not been synthesized, a three-letter symbol and corresponding name are temporary.

Table 1: Examples of element atomic symbols
Element Symbol

hydrogen

H

argon

Ar

potassium

K

sodium

Na

chlorine

Cl

ununseptium

Uus

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. Complex (or complicated) prefixes are not used in this class.

Table 2: Multiplicative prexfixes
No. Simple Complicated

1

mono


2

di

bis

3

tri

tris

4

tetra

tetrakis

5

penta

pentakis

6

hexa

hexakis

7

hepta

heptakis

8

octa

octakis

9

nona

nonakis

10

deca

decakis

11

undeca

undecakis

12

dodeca

dodecakis

20

icosa

icosakis

Homoatomic entities

Homoatomic entities are particles containing only one element. The name is determined by combining the element name with the proper multiplicative prefix (Table 2).

Names of molecules are constructed by using the appropriate prefix in front of the name of the element.

<prefix> <element name>


“Ion names contain their charge numbers in parenthesis and for most homoatomic anion names, ‘ide’ is added in place of the ‘en’, ‘ese’, ‘ic’ ‘ine’, ‘ium’, ‘ogen’, ‘on’, ‘orus’, ‘um’, ‘ur’, ‘y’ or ‘ygen’ endings of element names. Exceptions include Zn and Group 18 elements ending in ‘on’, where ‘the ’ide’ ending is added to the element names. Some elements, such as Fe, Ag, and Au, contain a Latin stem before the ‘ide’ ending. Some ions have acceptable traditional names that do not include charge numbers.”5

<prefix> <element name> (<charge>)


For homoatomic cation names, the element name followed by the charge number in parenthesis.

Table 3: Examples of homoatomic entities
Type Formula Name

Molecule

H2

dihydrogen

Molecule

N2

dinitrogen

Molecule

O2

dioxygen

Molecule

S8

octasulfur

Cation

H3+

trihydrogen(1+)

Cation

Na+

sodium(1+)

Cation

O2+

dioxygen(1+)

Cation

S42+

tetrasulfur(2+)

Cation

Hg22+

dimercury(2+)

Cation

Bi54+

pentabismuth(4+)

Cation

Fe3+

iron(3+)

Anion

H

hydride(1–) or hydride ion

Anion

N3

trinitride(1–) or nitride ion

Anion

O22–

dioxide(2–) or peroxide ion

Anion

F

fluoride(1–) or fluoride ion

Anion

Cl

chloride(1–) or chloride ion

Anion

I3

triiodide(1–) or triiodide ion

Monatomic ions

Monatomic ions are a subset of homoatomic entities. Monatomic ions contain only one atom with a charge.

The names of monatomic positive ions (metal cations) from Group 1 and 2, or aluminum, are commonly constructed from the name of the metal as well as its charge in parenthesis followed by the word ‘ion’ (Table 4). Sometimes the word ‘cation’ is used in place of ‘ion’.

<element name> (<charge>)


Transition metal ions can sometimes form more than one type of positive ion and has its oxidation state included as a Roman numeral in parenthesis immediately following the name of the metal. Note: “Oxidation state” is usually equivalent to “charge” in the context of ionic compounds but not equivalent in the context of molecules.

<transition metal element name> (<charge>)


The names of monatomic negative ions (anions of nonmetals) is named by adding ‘ide’ to the stem of the name of the nonmetal element from which the ion is derived.

<element name> (<charge>)

or

<root element name+ide>


Figure 1 shows the typical charge(s) some elements adopt when becoming an ion.

Figure 1: Typical charges of monatomic ions
Table 4: Examples of monatomic ions
Formula IUPAC Name
Monatomic positive ions

H+

hydrogen(1+)
hydron
proton (informally)

Li+

lithium(1+)

Na+

sodium(1+)

K+

potassium(1+)

Mg2+

magnesium(2+)

Ca2+

calcium(2+)

Al3+

aluminum(3+)

Transition metal ions

Co2+

cobalt(2+)

Fe3+

iron(3+)

Sc4+

scandium(4+)

Monatomic negative ions

H

hydrogen(1–) or hydride

S2–

sulfur(2–) or sulfide

N3–

nitrogen(3–) or nitride

F

fluoride(1–) or fluoride

Cl

chloride(1–) or chloride

Br

bromide(1–) or bromide

I

iodide(1–) or iodide

Some ions, many of which are from transition metals, have historic names based in Latin (Table 5).

Table 5: Examples of monatomic cations with Latin names
Formula Name Latin Name

Cu+

copper(I) ion

cuprous

Cu2+

copper(II) ion

cupric

Au+

gold(I) ion

aurous

Au3+

gold(III) ion

auric

Fe2+

iron(II) ion

ferrous

Fe3+

iron(III) ion

ferric

Pb2+

lead(II) ion

plumbous

Pb4+

lead(IV) ion

plumbic

Mn2+

manganese(II) ion

manganous

Mn3+

manganese(III) ion

manganic

Hg2+

mercury(II) ion

mercuric

K+

potassium ion

kalic

Ag+

silver ion

argentous

Na+

sodium ion

natric

Sn2+

tin(II) ion

stannous

Sn4+

tin(IV) ion

stannic

Example: FeCl2 can be called ferrous chloride. FeCl3 can be called ferric chloride.

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 6).

Table 6: Examples of polyatomic ions
Formula Name
Cations: Group 15

NH4+

ammonium ion
azanium

Cations: Group 16

H3O+

hydronium ion
oxonium ion
oxidane

Anions: Group 14

C22–

acetylide ion

CN

cyanide ion

CH3CO2 or CH3COO

acetate ion

CO32–

carbonate ion

HCOO

formate ion

C2H5O

ethoxide ion

C2O42–

oxalate ion

C6H5O73–

citrate ion

Anions: Group 15

N3

azide ion

Anions: Group 16

O2

superoxide ion

O22–

peroxide ion

OH

hydroxide ion

OCN

cyanate ion

SH

bisulfide ion

SCN

thiocyanate ion

Transition metals

CrO42–

chromate ion

Cr2O72–

dichromate ion

MnO4

permanganate ion

MnO42–

manganate ion

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 7 illustrate these naming schemes.

Table 7: Examples of oxyanions
Formula Name
Anions: Group 15

NO2

nitrite ion

NO3

nitrate ion

NO4

pernitrate ion

PO33–

phosphite ion

PO43–

phosphate ion

PO53–

perphosphate ion

Anions: Group 16

SO32–

sulfite ion

SO42–

sulfate ion

SO52–

persulfate ion

SeO32–

selenite ion

SeO42–

selenate ion

TeO32–

tellurite ion

TeO42–

tellurate 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

One strategy to remember the polyatomic oxyanions is to memorize each ion ending in ‘-ite’. Subsequent additions of oxygen (where appropriate) to the ion changes the suffix to ‘-ate’ and ‘per…ate’, respectively. The removal of one oxygen leads to ‘hypo…-ite’.

Polyatomic oxyanions that contain hydrogen are named by adding the word “hydrogen” before the name of the oxyanion.

Table 8: Examples of oxyanions containing hydrogen
Formula IUPAC Name Systematic Name Common Name
Anions: Group 14

HCO3

hydrogencarbonate

hydrogen carbonate ion

bicarbonate ion

Anions: Group 15

HPO42–

hydrogenphosphate

monohydrogenphosphate

hydrogen phosphate ion

H2PO4

dihydrogenphosphate

phosphoric acid, ion(1–)

dihydrogen phosphate ion

Anions: Group 16

HSO3

hydrogensulfite

hydrogen sulfite ion

bisulfite ion

HSO4

hydrogensulfate

hydrogen sulfate ion

bisulfate ion

Binary compounds

Binary compounds (those containing two elements) are arranged in the (reverse) order given in Figure 2. That is, the first encountered element is preceeded by the second encountered element.

Figure 2: Element sequence as provided by IUPAC5

The first encountered element is treated as being an anion (the more ‘electronegative’ element) and is given an ‘ide’ ending and placed after the name of the ‘electropositive’ element (treated as a cation) separated by a space.

If the compound is ionic:

  1. Elemental name of metal
  2. Elemental name of nonmetal with “ide” ending
  3. Metals that can adopt various oxidation states receive a Roman numeral in parenthesis indicating the oxidation state (preferred). Note that if the oxidation state is excluded, a prefix must be attached to the nonmetal (not preferred)
  4. Polyatomic ions retain their names (see Table 6)

If the compound is molecular,

  1. Element name of nonmetal
  2. Root element name of second nonmetal
  3. Omit “mono” for first element
  4. No prefix if first element is hydrogen
  5. Drop the second “o” in “mono” prior to a vowel
  6. Drop the “a” in prefixes ending in “a” prior to a vowel
Table 9: Examples of binary compounds
Type Formula IUPAC Name Systematic Name

Molecular

H2O2

hydrogen peroxide

peroxol

Molecular

HBr

hydrogen bromide

bromane

Molecular

CO

carbon monoxide

carbon monooxide

Molecular

CO2

carbon dioxide

dioxidocarbon

Molecular

N2H4

hydrazine

diazine

Molecular

PH3

phosphane or phosphine (common)

hydrogen phosphide

Molecular

NO

nitrogen monoxide

nitric oxide

Molecular

N2O

dinitrogen monoxide

nitrous oxide

Molecular

NO2

nitrogen dioxide


Molecular

NH3

ammonia

azane

Molecular

H2O

water

oxidane

Ionic

NaCl

sodium chloride


Ionic

FeCl2

iron(II) chloride
iron dichloride


Ionic

FeCl3

iron(III) chloride
iron trichloride


Ionic

Hg2Cl2

mercury(I) chloride
dimercury(I) chloride
dimercury dichloride


Ionic compounds

Ionic compounds (salts) are electrically neutral substances containing a combination of cations and anions. Typically, ionic compounds can be determined by the presence of a metal and a nonmetal though there are some exceptions to this such as the presence of a polyatomic cation (e.g. NH4Cl).

The names of ionic compounds are constructed from their cation and anion components. The positive cation name is given first followed by the name of the anion and separated by a space.

<cation element name> <root anion element name+ide>


If the cation is a transition metal, a parenthesized Roman numeral should immediately follow the name of the cation indicating the oxidation state of the cation. If there are more than one polyatomic ion of a given type, enclose the polyatomic ion in parenthesis followed by a subscript integer to denote the number of polyatomic ions present (e.g. Ca3(PO4)2)

<transition metal name>(<charge>) <root anion element name+ide>


Note that multiplicative prefixes are not used when naming ionic compounds. The number of cations and anions are inferred based on the charges of each (e.g. MgCl2 is magnesium chloride, not magnesium dichloride). Exception: When transition metals are involved, multiplicative prefixes are used if, and only if, a Roman numeral indicating the oxidation state of the transition metal is not present; however, Roman numerals are preferred.

Hydrates are substances that contain water. Their chemical formulas include the number of water molecules present after the compound separated by a center dot. Use multiplicative prefixes to denote the number of water molecules in the hydrate. Note: Compounds containing fractional waters of 0.5 and 1.5 per unit cell (called hemihydrates) have prefixes of “hemi” and “sesqui”, respectively. Compounds resulting from the removal of water from their corresponding hydrates are called anhydrous.

<ionic compound name>·<prefix+hydrate>


Table 10: Examples of ionic compounds
Formula IUPAC name

NaCl

sodium chloride

KBr

potassium bromide

MgCl2

magnesium chloride

CaBr2

calcium bromide

Ca3(PO4)2

calcium phosphate

Al2O3

aluminum oxide

FeCl3

iron(III) chloride
iron trichloride

Co2O3

colbalt(III) oxide
dicobalt trioxide

NH4Cl

ammonium chloride

(NH4)2O

ammonium oxide

(NH4)2CO3

ammonium carbonate

FeCl2

iron(II) chloride
iron dichloride

FeCl3

iron(III) chloride
iron trichloride

CoCl2

cobalt(II) chloride
anhydrous colbalt(II) chloride
cobalt dicholoride

CoCl2·6H2O

cobalt(II) chloride hexahydrate
cobalt dichloride hexahydrate

CaSO4·0.5H2O

calcium sulfate hemihydrate

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 11).

Table 11: 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

13

tridec

14

tetradec

15

pentadec

16

hexadec

17

heptadec

18

octadec

19

nonadec

20

icos

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 12: Examples of linear alkanes
Number of Carbons Formula IUPAC Name Alternative Name

1

CH4

methane

n-methane

2

C2H6

ethane

n-ethane

3

C3H8

propane

n-propane

4

C4H10

butane

n-butane

5

C5H12

pentane

n-pentane

6

C6H14

hexane

n-hexane

7

C7H16

heptane

n-heptane

8

C8H18

octane

n-octane

9

C9H20

nonane

n-nonane

10

C10H22

decane

n-decane

11

C11H24

undecane

n-undecane

12

C12H26

dodecane

n-dodecane

Alkenes

Alkenes are unsaturaeted hydrocarbons where there exists a double bond between two carbon atoms in the molecule. The naming is similar to alkanes such that the organic prefixes in Table 11 are used to denote the number of carbon atoms present. The suffix ‘ene’ is attached to the prefix. Leading integers followed by a hyphen are used to denote the position of the double bond in a carbon chain, identified by counting to the first carbon atom involved in the double bond. If the double bond is at the first carbon for straight chain alkenes beyond propene, the “1-” is often omitted.

Structural isomers of butene


Butene (C4H8) exists as as various structural isomers. Three are given below. Two structural isomers of 2-butene exist and distinguished by using the prefix ‘cis-’ and ‘trans-’ depending on the torson angle about the central bond. A torsion of 0° is labeled as ‘cis’ whereas a torsion angle of 180° is labeled as ‘trans’.

Click the dropdowns to see the skeletal formulas (line structures).

1-butene

Preferred IUPAC name: but-1-ene

cis-2-butene

Preferred IUPAC name: (2Z)-but-2-ene

trans-2-butene

Preferred IUPAC name: (2E)-but-2-ene

Table 13: Examples of linear alkenes with a double bond at the first carbon
Number of Carbons Formula IUPAC Name Systematic Name Common Name

2

C2H4

ethene

ethene

ethylene

3

C3H6

propene

propene

propylene

4

C4H8

1-butene

but-1-ene

butylene

5

C5H10

1-pentene

pent-1-ene

pentylene

6

C6H12

1-hexene

hex-1-ene

hexylene

Alkynes

Alkynes are unsaturated hydrocarbons containing at least one carbon-carbon triple bond. Naming is similar to that of alkanes and alkenes (uses organic prefixes, number denotes position of triple bond, etc.). Names end in ‘yne’.

Table 14: Examples of linear alkynes with a triple bond at the first carbon
Number of Carbons Formula IUPAC name Systematic name

2

C2H2

acetylene

ethyne

3

C3H4

allyene

propyne

4

C4H6

1-butyne

but-1-yne

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 11) associated with the number of carbon atoms followed by “anol” as the suffix. The leading “1-” can be excluded.

Table 15: Examples of linear alcohols
Numbe of Carbons Formula Condensed Formula IUPAC Name Alternative Name

1

CH4O

CH3OH

methanol

1-methanol

2

C2H6O

C2H5OH

ethanol

1-ethanol

3

C3H8O

C3H7OH

propanol

1-propanol

4

C4H10O

C4H9OH

butanol

1-butanol

5

C5H12O

C5H11OH

pentanol

1-pentanol

6

C6H14O

C6H13OH

hexanol

1-hexanol

7

C7H16O

C7H15OH

heptanol

1-heptanol

8

C8H18O

C8H17OH

octanol

1-octanol

9

C9H20O

C9H19OH

nonanol

1-nonanol

10

C10H22O

C10H21OH

decanol

1-decanol

11

C11H24O

C11H23OH

undecanol

1-undecanol

12

C12H26O

C12H25OH

dodecanol

1-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 11) associated with the number of carbon atoms followed by “anoic” as the suffix and terminate the name with the word “acid”.

Table 16: Examples of carboxylic acids
Number of Carbons Formula Condensed Formula IUPAC Name Common Name

1

CH2O2

HCOOH

methanoic acid

formic acid

2

C2H4O2

CH3COOH

ethanoic acid

acetic acid

3

C3H6O2

CH3CH2COOH

propanoic acid

proionic acid

4

C4H8O2

CH3CH2CH2COOH

butanoic acid

butyric acid

5

C5H10O2

CH3(CH2)3COOH

pentanoic acid

propylacetic acid

6

C6H12O2

CH3(CH2)4COOH

hexanoic acid

caproic acid

7

C7H14O2

CH3(CH2)5COOH

heptanoic acid

enanthic acid

8

C8H16O2

CH3(CH2)6COOH

octanoic acid

caprylic acid

9

C9H18O2

CH3(CH2)7COOH

nonanoic acid

pelargonic acid

10

C10H20O2

CH3(CH2)8COOH

decanoic acid

capric acid

11

C11H22O2

CH3(CH2)9COOH

undecanoic acid

undecylic acid

12

C12H24O2

CH3(CH2)10COOH

dodecanoic acid

lauric acid

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.