Question

Name the following ionic compounds using the Stock system: (a) \(\mathrm{Mn}_{2} \mathrm{O}_{3}\) (b) \(\mathrm{Hg}_{2} \mathrm{Cl}_{2}\), (c) \(\mathrm{PbS}\), (d) \(\mathrm{CrCl}_{3} \cdot 4 \mathrm{H}_{2} \mathrm{O}\)

Short answer

The names of the ionic compounds using the Stock system are: (a) manganese(III) oxide, (b) mercury(I) chloride, (c) lead(II) sulfide, (d) chromium(III) chloride tetrahydrate.

Step-by-step solution

Determine the charge of the metal cation in \(\mathrm{Mn}_{2}\mathrm{O}_{3}\)

The compound is composed of manganese (Mn) and oxygen (O). Since oxygen has a charge of -2 and there are three oxygen atoms, the total negative charge is -6. To neutralize, the two manganese atoms must have a total charge of +6. Therefore, each Mn atom has a charge of +3.

Write the ionic compound name for \(\mathrm{Mn}_{2}\mathrm{O}_{3}\)

Using the Stock system, manganese's charge is indicated with a Roman numeral in parentheses. The name of the compound is manganese(III) oxide.

Determine the charge of the metal cation in \(\mathrm{Hg}_{2}\mathrm{Cl}_{2}\)

The compound contains mercury (Hg) and chlorine (Cl). Usually, chlorine has a charge of -1, and there are two chlorine atoms, so the total charge is -2. Since \(\mathrm{Hg}_{2}^{2+}\) acts as a single cation with a +2 charge, each Hg atom has an effective charge of +1.

Write the ionic compound name for \(\mathrm{Hg}_{2}\mathrm{Cl}_{2}\)

Using the Stock system, mercury's charge is indicated with a Roman numeral. However, for mercury(I), the notation \(\mathrm{Hg}_{2}^{2+}\) is used rather than \(\mathrm{Hg}^{+}\). The name of the compound is mercury(I) chloride.

Determine the charge of the metal cation in \(\mathrm{PbS}\)

Lead (Pb) forms multiple cations, but sulfur (S) always has a charge of -2. Because there is only one sulfur, lead must have a charge of +2 to balance the charge.

Write the ionic compound name for \(\mathrm{PbS}\)

Since lead has a charge of +2 in this compound, the Stock system name will include a Roman numeral. The name is lead(II) sulfide.

Determine the charge of the metal cation in \(\mathrm{CrCl}_{3} \(4 \mathrm{H}_{2}\mathrm{O}\)\)

Chromium (Cr) is the cation and chlorine (Cl) is the anion. With three chloride ions, each with a charge of -1, the total charge is -3. Chromium must have a charge of +3 to balance the chloride ions. The water molecules (hydrates) do not affect the charge.

Write the ionic compound name for \(\mathrm{CrCl}_{3} \(4 \mathrm{H}_{2}\mathrm{O}\)\)

The name of the anhydrous part is chromium(III) chloride using the Stock system. Because there are four water molecules associated, it is a hydrate. The compound name is chromium(III) chloride tetrahydrate.

Key concepts

Stock System

The Stock system is a widely used methodology in chemistry to name ionic compounds, specifically those involving a metal with variable oxidation states.

It utilizes Roman numerals within parentheses to indicate the oxidation state, or charge, of the metal ion in the compound. This system is vital for compounds where metals can exhibit more than one oxidation state, such as many transition metals. For instance, the manganese ion in manganese(III) oxide, (Mn₂O₃), has an oxidation state of +3. Similarly, in lead(II) sulfide (PbS), the lead ion carries a +2 charge.

Mastering the Stock system provides clarity and precision in chemical communication, preventing confusion over which charged species is present in a compound.

Chemical Nomenclature

Chemical nomenclature, the formal system of naming chemical compounds, is essential for scientists to convey information accurately and efficiently.

The rules for naming ionic compounds, like those highlighted in the Stock system, help distinguish between the possible charges of the ions involved. When using the Stock system for metals with multiple ionic forms, the specific ionic charge is indicated after the metal's name. For example, mercury(I) chloride identifies that each mercury possesses a +1 charge. Similarly, chromium(III) chloride clarifies that the chromium has a +3 charge.

The precision in naming extends to complexes too, such as indicating water of hydration in hydrates. A compound like (CrCl₃ · 4H₂O) is named chromium(III) chloride tetrahydrate, showing it contains four water molecules.

Oxidation States

Oxidation states, or oxidation numbers, reveal the degree of oxidation of an atom in a chemical compound. Understanding oxidation states is crucial for balancing chemical equations, determining electron flow in redox reactions, and naming compounds.

In ionic compounds, the sum of the oxidation states must equal the compound's overall charge. For example, in manganese(III) oxide (Mn₂O₃), the oxidation state of manganese is +3, which balances the -2 charge of each oxygen atom. In naming, these oxidation states guide the use of Roman numerals in the Stock system. Correctly determining the oxidation state of elements within compounds is thus foundational to understanding their chemical behavior.

Transition Metal Chemistry

Transition metal chemistry is characterized by the presence of elements with partially filled d-orbitals, often leading to the possibility of multiple oxidation states and complex ion formation. This feature distinguishes transition metals from other elements and influences properties like color, magnetic behavior, and reactivity.

For instance, chromium in chromium(III) chloride tetrahydrate has a +3 oxidation state, which is critical to acknowledge in chemical reactions and nomenclature. The variable charges of transition metals also require the use of the Stock system in naming. By understanding transition metal chemistry, students can grasp the reactions that produce compounds and their naming conventions more thoroughly.