Question

Each of the following compounds is incorrectly named. What is wrong with each name, and what is the correct name for each compound? a. ${\mathrm{FeCl}}_3$, iron chloride b. ${\mathrm{NO}}_2$, nitrogen(IV) oxide c. $\mathrm{CaO}$, calcium(II) monoxide d. ${\mathrm{Al}}_2{\mathrm{S}}_3$, dialuminum trisulfide

Short answer

The correct names for each compound are: a. ${\mathrm{FeCl}}_3$: iron (III) chloride b. ${\mathrm{NO}}_2$: nitrogen dioxide c. $\mathrm{CaO}$: calcium oxide d. ${\mathrm{Al}}_2{\mathrm{S}}_3$: aluminum sulfide

Step-by-step solution

a. ${\mathrm{FeCl}}_3$, iron chloride

The given compound is a transition metal bonded with a non-metal, so we need to mention the oxidation state of the metal ion using Roman numerals. In this case, $\mathrm{Fe}$ has an oxidation state of +3, therefore the correct name is: iron (III) chloride.

b. ${\mathrm{NO}}_2$, nitrogen(IV) oxide

The given compound is a binary compound between two non-metals. The correct way to name this compound is to use prefixes to indicate the number of each element, and in the case of first element only, we don't use the prefix 'mono'. Therefore, the correct name is: nitrogen dioxide.

c. $\mathrm{CaO}$, calcium(II) monoxide

The given compound is an ionic compound between a metal and a non-metal. $\mathrm{Ca}$ has a fixed oxidation state and does not require the use of Roman numerals, therefore the correct name is: calcium oxide.

d. ${\mathrm{Al}}_2{\mathrm{S}}_3$, dialuminum trisulfide

The given compound is an ionic compound between a metal and a non-metal, so prefixes are not used here. $\mathrm{Al}$ has a fixed oxidation state and does not require the use of Roman numer of oxidation state. Therefore, the correct name is: aluminum sulfide.

Key concepts

Oxidation States

Understanding the concept of oxidation states is pivotal in correctly naming chemical compounds. Oxidation states, often referred to as oxidation numbers, tell us about the degree of oxidation of an atom in a compound. This value is expressed as an integer, which can be positive, negative, or zero, indicating the number of electrons lost or gained by an atom in comparison to its neutral state.

An element's oxidation state is crucial when naming compounds with transition metals, as the same metal can exhibit different oxidation states, leading to compounds with different properties. For instance, the solution indicates that iron in ${\mathrm{FeCl}}_3$ has an oxidation state of +3, justifying the name iron (III) chloride. In chemical nomenclature, Roman numerals are used to denote the oxidation state of elements, particularly transition metals, to avoid confusion due to their variable valence.

Ionic Compounds

Ionic compounds are composed of ions that are held together by ionic bonds, which arise from the attraction between positively charged metal ions (cations) and negatively charged non-metal ions (anions). These compounds are typically formed when metals react with non-metals, resulting in the transfer of electrons from the metal to the non-metal. This electron transfer creates ions that bond together electrostatically.

In naming ionic compounds, which include many salts, oxides, and minerals, the metal's name is stated first, followed by the non-metal with its ending changed to '-ide'. If the metal has a fixed oxidation state, like calcium in $\mathrm{CaO}$, it is simply called calcium oxide, without the need for specifying the oxidation state. Prefixes are not used in naming ionic compounds, thus ${\mathrm{Al}}_2{\mathrm{S}}_3$ is correctly named aluminum sulfide, not dialuminum trisulfide.

Binary Compounds

Binary compounds consist of two distinct elements. These elements can be either metals and non-metals, as seen in ionic compounds, or they can both be non-metals, such as in the compound ${\mathrm{NO}}_2$. When the compound comprises two non-metals, prefixes are used to denote the number of atoms of each element present in the compound, except for the first element if it has a single atom, which is why the correct name for ${\mathrm{NO}}_2$ is nitrogen dioxide.

The prefixes mono-, di-, tri-, and so on, are appended to the name of the element to represent one, two, three, etc., atoms of that element within the compound. This method of nomenclature helps differentiate between different ratios of combined non-metals, which can result in compounds with varying characteristics despite being formed from the same elements.

Transition Metals

Transition metals are elements found in the central block of the periodic table, known for their ability to display a range of oxidation states, which gives them a fascinating and complex chemistry. This ability stems from the proximity in energy levels of their outermost and penultimate shells of electrons.

When naming compounds containing transition metals, it is essential to specify the metal's oxidation state because they can form multiple stable ions. For example, iron can exist as Fe²⁺ or Fe³⁺, leading to different compounds, such as iron (II) chloride or iron (III) chloride for ${\mathrm{FeCl}}_2$ and ${\mathrm{FeCl}}_3$, respectively. This specificity is a key characteristic of chemical nomenclature involving transition metals. Furthermore, while some transition metals like zinc and silver have consistent oxidation states, the majority require the oxidation state to be included in the compound's name to ensure proper identification.