IUPAC Nomenclature of Chemical Compounds

NAMING OF BINARY COMPOUNDS

Nomenclature refers to the essential system utilized for assigning names to chemical compounds. The primary authority responsible for developing and maintaining this system is the International Union of Pure and Applied Chemistry (IUPAC). IUPAC’s nomenclature guidelines play a crucial role in ensuring uniformity and clarity in the naming of chemical substances.

The process of naming chemical compounds involves considering the constituent elements present in the compound and, if necessary, taking into account their oxidation numbers. This systematic approach helps in identifying and differentiating various compounds, thereby facilitating effective communication among scientists and researchers.

When naming binary compounds consisting of only two elements, a specific order is followed. The electropositive elements, commonly known as cations, are typically named first. These elements possess a tendency to lose electrons and form positive ions. Conversely, the electronegative elements, referred to as anions, come last in the name and are modified with the addition of the suffix “-ide.” Electronegative elements have a higher affinity for electrons, leading them to gain electrons and form negative ions.

By adhering to this naming convention, chemists can accurately and consistently identify the composition and structure of various compounds, enabling effective communication and comprehension in the field of chemistry. The IUPAC’s nomenclature guidelines continue to serve as a vital resource for scientists worldwide, promoting standardization and facilitating a better understanding of chemical compounds.

Examples:

Formula               IUPAC name

MgO                  Magnesium oxide

H₂S                    Hydrogen sulphide

NH₄Cl                Ammonium chloride

NaH                   Sodium hydride

But in cases where the two elements involved are non-metals, the above rule is not followed. For example, H₂O (water) NH₃ (ammonia) and PH₃ (phosphine)

NAMING OF RADICALS AND COMPOUNDS HAVING ELEMENTS WITH VARIABLE OXIDATION NUMBERS

When naming compounds that contain radicals, which are groups of atoms of elements carrying an electrical charge, they are treated as a single entity. This simplifies the process of naming and categorizing these compounds. The naming conventions for compounds with radicals follow similar principles to those used for binary compounds.

In the nomenclature of compounds containing radicals, the name of the radical is often written first, followed by the name of the other constituent elements. This helps to emphasize the unique characteristics and behavior of the radical within the compound. The charge of the radical is indicated by using appropriate numerical prefixes such as mono-, di-, tri-, and so on, to specify the number of radicals present.

For example, consider the compound sodium hydroxide (NaOH), which contains the hydroxide radical (-OH). In this case, the radical is named first, followed by the name of the cation, sodium. This naming convention highlights the hydroxide radical’s presence and its significance in the compound.

Furthermore, in compounds with polyatomic radicals, it is common to retain the original name of the radical, as these radicals often have well-established names. Examples include sulfate (SO4²⁻), nitrate (NO3⁻), and ammonium (NH4⁺).

By treating radicals as single elements during naming, chemists can effectively communicate the composition and structure of compounds containing these groups of atoms. This approach simplifies the naming process while preserving the unique identity and reactivity of the radicals within the compound.

Examples of radicals with their names are as follows:

Radical                            IUPAC NAME

NH4⁺                            Ammonium ion

OH^‑                                        Hydroxyl ion

But in naming acid radicals, the oxidation number of elements is indicated by Roman numbers in bracket.

Example:

Formula             IUPAC

NO₂‑                  Dioxonitratei(iii) ion

NO₃^–                   Trioxonitrate(v) ion

CO₃^2-                 Trioxocarbonate(iv) ion.

Also, the compounds having elements with Roman numbers in brackets indicating their oxidation numbers in that compound

Examples

Formula                   IUPAC

FeO                          Iron (ii) oxide

Cu₂O                        Copper (i) oxide

MgCO₃                     Magnesium trioxocarbonate (iv)

NAMING TERTIARY COMPOUNDS AND QUARTENARY COMPOUNDS

These are compounds containing more than two elements.

Examples are oxo-acids, normal salts, and acid salts.

Acid                                 IUPAC

HNO₃                              Trioxonitrate(v) acid

H₂SO₄                             Tetraoxosulphate (vi) acid

H₃PO₄                             Tetraoxophospate (v) acid

Examples of Normal Salts.

Normal salts                      IUPAC

KNO₃                               Potassium trioxonitrate (iv)

NaSO₄                             Sodiumtetraoxosulphate (vi)

CuCO₃                              Copper (ii) trioxocarbonate (iv)

NAMING OF COMPOUNDS WHOSE CATIONS HAVE BEEN PARTIALLY REPLACED WITH HYDROGEN IONS.

In naming compounds whose cations have been partially replaced with a hydrogen ion, the cations are named first followed by hydrogen, then the radicals present indicating the Roman number standing for the oxidation number of the element that is combined with oxygen to form the radical.

E.g Formula                                IUPAC

NaHSO₄                                       Sodium hydrogen tetraoxosulphate (vi)

KHSO₃                                        Potassium hydrogen trioxosulphate (iv)

Read also:

PARTICULATE NATURE OF MATTER

STANDARD SEPARATION TECHNIQUES

COMPOUNDS AND MIXTURES

ELEMENTS, SYMBOLS & VALENCY

NATURE OF MATTER