Question

Name the following ionic compounds using the Stock system: (a) FeS, (b) \(\mathrm{CuO}\) (c) \(\mathrm{SnO}_{2}\), (d) \(\mathrm{CoCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O} .\)

Short answer

The ionic compounds named using the Stock system are: (a) iron(II) sulfide, (b) copper(II) oxide, (c) tin(IV) oxide, (d) cobalt(II) chloride hexahydrate.

Step-by-step solution

Understanding the Stock System

The Stock system is a method of naming that uses Roman numerals to represent the valency (or charge) of the metal cation in an ionic compound. In the Stock system, the metal's name is followed by its charge in parentheses in Roman numerals.

Determining the Charge of the Iron Cation in FeS

In the compound FeS, sulfur commonly has a charge of -2 as an anion. Since the compound is neutral overall, the iron cation must balance this with a charge of +2. Therefore, the name of FeS using the Stock system is iron(II) sulfide.

Naming Copper(II) Oxide

For the compound CuO, copper must have a +2 charge to balance the -2 charge of the oxygen anion. Thus, the correct name is copper(II) oxide.

Naming Tin(IV) Oxide

In the compound SnO2, each oxygen anion has a -2 charge, making a total of -4. To balance this, tin must have a +4 charge, leading to the name tin(IV) oxide.

Naming Cobalt(II) Chloride Hexahydrate

For the compound CoCl2·6H2O, chloride has a -1 charge and there are two chloride anions, for a total of -2. Consequently, cobalt must have a + mes with the hexahydrate indicating six water molecules. Therefore, the name is cobalt(II) chloride hexahydrate.

Key concepts

Chemical Nomenclature

Chemical nomenclature is a systematic method for naming chemical compounds and is crucial for effective communication within the scientific community.

In the context of ionic compounds, nomenclature involves identifying the positive and negative ions (cations and anions) and accounting for their charges to ensure that the compound is electrically neutral. Each element has a standard name, but many elements, especially metals, can form ions with different charges, leading to different compounds. Hence, a systematic naming convention, such as the Stock system, is necessary to clearly distinguish between these compounds.

As seen with the compound FeS, rather than just calling it 'iron sulfide', which could be ambiguous due to different possible iron charges, the Stock system clarifies the compound as iron(II) sulfide, indicating that iron is in the +2 oxidation state.

Valency of Metals

The valency of metals is a measure of an element's combining power with other atoms when it forms chemical compounds or molecules. It corresponds to the charge of the ions that metals form and is critical for determining the formula of the compounds they will create.

The valency is often equivalent to the number of electrons an atom loses, gains, or shares when it reacts. For example, the valency of iron in iron(II) sulfide is 2, which signifies that the iron ion donates two electrons to achieve a stable electronic configuration.

Understanding the valency is fundamental when using the Stock system; it informs the Roman numeral used in the compound's name. This level of precision helps avoid confusion, particularly when an element can have more than one common valency, such as copper in copper(I) oxide and copper(II) oxide.

Roman Numerals in Chemistry

Roman numerals in chemistry serve the purpose of indicating the oxidation state (or valency) of an element, particularly a metal cation, in a compound.

The usage of Roman numerals is standard practice in the Stock system of nomenclature. When writing the name of an ionic compound, the cation’s name is followed by its charge in Roman numerals in parentheses. This is exemplified in the name iron(II) sulfide, where 'II' denotes that iron has a +2 charge, distinguishing it from other potential iron sulfides.

Importance of Accuracy

Accurate use of Roman numerals is essential for precision in scientific communication. Confusing a 'II' (2) with a 'III' (3) could refer to a completely different compound with distinct properties.

By mastering the Roman numeral system, students can accurately interpret and construct the chemical names of compounds, ensuring clarity and reducing the risk of errors.