Question

Each of the following compounds has three possible names listed for it. For each compound, what is the correct name and why aren't the other names used? a. \(\mathrm{N}_{2} \mathrm{O}\) : nitrogen oxide, nitrogen(I) oxide, dinitrogen monoxide b. \(\mathrm{Cu}_{2} \mathrm{O}\) : copper oxide, copper(I) oxide, dicopper monoxide c. \(\mathrm{Li}_{2} \mathrm{O}\) : lithium oxide, lithium(I) oxide, dilithium monoxide

Short answer

The correct names for the compounds are: a. N₂O: dinitrogen monoxide, as it indicates the number of each element present and distinguishes it from other nitrogen oxides. b. Cu₂O: copper(I) oxide, as it specifies the oxidation state of copper, which is +1, making it clearer and more common than dicopper monoxide. c. Li₂O: lithium oxide, as there is only one possible oxidation state for lithium, and it is a shorter, unambiguous, and more commonly used term compared to dilithium monoxide.

Step-by-step solution

a. N₂O: nitrogen oxide, nitrogen(I) oxide, dinitrogen monoxide

The correct name for the compound N₂O is dinitrogen monoxide. Following IUPAC rules, the prefix "di-" is used to indicate there are two nitrogen atoms, and "mono-" is used to indicate there is one oxygen atom. Nitrogen oxide is an ambiguous term since there are various oxides of nitrogen that could be referred to by this name. Nitrogen(I) oxide is incorrect because the oxidation state of nitrogen in N₂O is not +1. The Roman numeral in parentheses is used to indicate the oxidation state, and in N₂O, each nitrogen atom has an oxidation state of +1, but the compound overall has +2 oxidation state.

b. Cu₂O: copper oxide, copper(I) oxide, dicopper monoxide

The correct name for the compound Cu₂O is copper(I) oxide. In this case, the Roman numeral in parentheses indicates the oxidation state of the copper atom, which is indeed +1. Copper oxide is an ambiguous term that could refer to CuO (copper(II) oxide) as well. Dicopper monoxide is not incorrect per se, but using the oxidation state as in copper(I) oxide is a more common and clearer way of identifying this compound.

c. Li₂O: lithium oxide, lithium(I) oxide, dilithium monoxide

The correct name for the compound Li₂O is lithium oxide. In this case, lithium has only one possible oxidation state (+1), so we do not need to specify it. Therefore, lithium(I) oxide would not be incorrect, but it is unnecessary and redundant. Dilithium monoxide is also a correct name following the IUPAC rules to indicate there are two lithium atoms and one oxygen atom, but lithium oxide is shorter, unambiguous, and more commonly used.

Key concepts

IUPAC Naming Conventions

Understanding the International Union of Pure and Applied Chemistry (IUPAC) naming conventions is essential for accurately identifying chemical compounds. These conventions provide a systematic way of naming chemicals so that their composition and structure are clear to anyone familiar with the system.

In IUPAC naming, prefixes such as 'mono-', 'di-', 'tri-', etc., indicate the number of atoms of an element in a compound. For example, 'dinitrogen' signifies two nitrogen atoms. Names also include suffixes like '-oxide', which specify the type of compound, in this case, an oxide. However, using generic terms like 'nitrogen oxide' can be misleading because several oxides containing nitrogen exist, such as NO, NO₂, and N₂O₃, each with distinct properties.

Moreover, where different oxidation states of an element are possible, as in the case of copper, the IUPAC naming includes the oxidation state in Roman numerals. Hence, 'copper(I) oxide' clearly identifies Cu₂O, separating it from other possibiliites such as CuO, which is 'copper(II) oxide'. In summary, the IUPAC nomenclature provides clarity in communication among chemists when discussing various compounds.

Oxidation States

Oxidation states play a crucial role in determining the correct name for chemical compounds under IUPAC conventions. An oxidation state is a number assigned to an element in a chemical compound representing the number of electrons lost or gained by an atom of the element in the compound.

For instance, in the compound N₂O, the oxidation states of the nitrogen atoms are not +1 as 'nitrogen(I) oxide' would suggest. In reality, both nitrogen atoms share a +2 oxidation state in aggregate, due to the particular bonding in the molecule. Similarly, the oxidation state of copper in Cu₂O is +1, which is why the name contains '(I)' to reflect this fact. Including the oxidation state not only provides chemical insight but also avoids confusion with similar compounds having different properties.

It's worth noting that for elements like lithium that have only one common oxidation state (+1), the inclusion of the state in the name is optional. Thus, 'lithium oxide' suffices without the need for '(I)', emphasizing that simplicity and accuracy are key in chemical nomenclature.

Chemical Compounds

Chemical compounds are substances formed when two or more elements combine chemically in fixed ratios. They possess unique properties that are different from those of the individual elements that compose them. The process of naming compounds takes into account various factors, including the elements involved, their proportions, and the type of chemical bond.

For every compound, a specific and unambiguous name can be ascertained using IUPAC rules. Prefixes are used to denote the number of atoms of each element in a molecule, while suffixes and infixes denote the nature of the compound and its bonding. With a clear system for identifying compounds, it's easier to understand their functionality and reactivity.

Taking into account the exercise, for instance, Li₂O is simply called 'lithium oxide' because it's the most straightforward representation of the compound's composition. Understanding these conventions can significantly enhance the communication and study of chemistry, making it a vital skill for students and professionals alike.