IUPAC Nomenclature For Inorganic Substances
This is part of preliminary HSC Chemistry course under the topic of Bonding.
HSC Chemistry Syllabus
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investigate the nomenclature of inorganic substances using International Union of Pure and Applied Chemistry (IUPAC) naming conventions
- Investigate the differences between ionic and covalent compounds through: Using nomenclature, valency, and chemical formulae (including Lewis dot diagrams) (ACSCH029)
Nomenclature of Inorganic Covalent & Ionic Substances
Ionic Compound Nomenclature
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Naming Protocol: the cation is typically named first, followed by the anion. For instance, in the ionic compound NaCl, the cation is the metal Sodium, while the anion is the non-metal Chlorine.
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Suffix Change: When the anion is a single non-metal, its name generally concludes with the suffix "-ide". Hence, for the ionic compound NaCl, it would be named sodium chloride, where 'chlorine' is replaced with 'chloride'.
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Polyatomic Anion: If the anion is polyatomic, its suffix remains unchanged. For example, CaCO3 is named calcium carbonate.
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Polyatomic Cation: When the cation is polyatomic, the same naming rules apply. For instance, NH4Cl is named ammonium chloride.
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Transition metals, capable of forming ions with varying charges, necessitate the charge indication by inserting a Roman numeral within parentheses after the metal name. For example, iron oxide, comprising of Fe and O, can be ambiguous as iron can exist as either `Fe^{2+}` or `Fe^{3+}` oxidation state, altering the compound formula to either `FeO` or `Fe_2O_3`. Therefore, if the iron ion is `Fe^{3+}`, the formula would be `Fe_2O_3`, named as iron(III) oxide. Conversely, if the iron ion is `Fe^{2+}`, the formula would be FeO, and it would be named iron(II) oxide.
Example 1
What is the name for the ionic compound with the formula MgCl2?
The cation is magnesium and the anion is chlorine (chloride). Since we do not need to provide any prefix to denote the number of atoms for each element in an ionic compound, the name is magnesium chloride.
Example 2
What is the name for the ionic compound with the formula Na2S?
The cation is sodium and the anion is sulfur (sulfide). Since we do not need to provide any prefix to denote the number of atoms for each element in an ionic compound, the name is sodium sulfide.
Example 3
What is the name for the ionic compound with the formula CuCl2?
The cation is copper and the anion is chlorine (chloride). Copper is a transition metal with various oxidation states. In this case, the oxidation state of copper is +2 because the empirical formula suggests the ratio between copper and chlorine in the compound is 1:2.
The name of this compound is copper(II) chloride.
Example 4
What is the name for the ionic compound with the formula CaSO4?
The cation is calcium and the anion is a polyatomic ion sulfate. The name of this compound is calcium sulfate.
Covalent Compound Nomenclature
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Naming Order: For covalent compounds, the less electronegative element is usually named first. This rule will typically be provided.
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Utilising Prefixes: Numerical prefixes like mono, di, tri, tetra, and so on are used to indicate the number of atoms of each element in the compound. If there is only one atom for the first element in the name, the prefix mono- is not necessary. This is the major difference between nomenclature of ionic and covalent compounds.
- Addition of Suffix: The name of the compound generally ends with the suffix "-ide" or "-ine".
Example 1
Consider a compound consisting of two atoms of oxygen and one atom of nitrogen (NO2).
As nitrogen is less electronegative, it is named first, followed by the prefix 'di-' for two oxygen atoms, leading to 'dioxide'. The prefix 'mono-' is not required for nitrogen because it is the first element in the name.
Hence, the compound NO2 is named nitrogen dioxide.
Example 2
Consider a compound consisting of four atoms of oxygen and two atoms of nitrogen (N2O4).
As nitrogen is less electronegative, it is named first with a prefix 'di-'. This is followed by the prefix 'tetra-' for two oxygen atoms, leading to 'tetroxide'.
Hence, the compound N2O4 is named dinitrogen tetroxide.
Example 3
Consider a compound consisting of two chlorine and seven oxygen atoms (Cl2O7).
Chlorine being the less electronegative element is named first, using the prefix "di-" for two atoms, leading to 'dichlorine', and then the prefix "hepta-" for seven oxygen atoms, forming 'heptoxide'.
Therefore, the compound Cl2O7 is named dichlorine heptoxide.