Name | Molecular Formula | Structural Formula | Konnectivity Formula* | Stereochemical Formula |
---|---|---|---|---|
Methane |
CH4 |
CH4 |
||
Ethanol |
C2H6O |
CH3CH2OH |
||
Diethyl ether |
C2H6O |
CH3OCH3 |
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.
- Overall summary of chemical nomenclature (PDF)1
- Inorganic compounds (the Red Book; PDF)2
- Organic compounds (the Blue Book; PDF)3
- Polymers (the Purple Book; PDF)4
Molecular models
Molecules can be represented in various ways.
*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.
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.
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.
“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
For homoatomic cation names, the element name followed by the charge number in parenthesis.
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’.
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.
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.
or
Figure 1 shows the typical charge(s) some elements adopt when becoming an ion.
Monatomic positive ions | |
---|---|
Transition metal ions | |
Monatomic negative ions | |
Some ions, many of which are from transition metals, have historic names based in Latin (Table 5).
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).
Cations: Group 15 | |
---|---|
Cations: Group 16 | |
Anions: Group 14 | |
Anions: Group 15 | |
Anions: Group 16 | |
Transition metals | |
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:
Table 7 illustrate these naming schemes.
Anions: Group 15 | |
---|---|
Anions: Group 16 | |
Anions: Group 17 | |
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.
Anions: Group 14 | |||
---|---|---|---|
Anions: Group 15 | |||
Anions: Group 16 | |||
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.
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:
- Elemental name of metal
- Elemental name of nonmetal with “ide” ending
- 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)
- Polyatomic ions retain their names (see Table 6)
If the compound is molecular,
- Element name of nonmetal
- Root element name of second nonmetal
- Omit “mono” for first element
- No prefix if first element is hydrogen
- Drop the second “o” in “mono” prior to a vowel
- Drop the “a” in prefixes ending in “a” prior to a vowel
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.
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)
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.
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).
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.
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
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’.
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.
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”.