Question

For a metallic element that forms two stable cations, the ending _______ is sometimes used for the cation with the lower charge.

Short answer

The ending '-ous' is sometimes used for the cation with the lower charge in metallic elements that form two stable cations.

Step-by-step solution

Recall the Nomenclature Rules for Ionic Compounds with Variable Charges

For metallic elements with variable charges, the Stock system is used to name the cations. With the Stock system, roman numerals are written in parentheses right after the cation to indicate its charge.

Identify the Ending for Cations with Lower Charge

When a metallic element forms two stable cations, the ending '-ous' is sometimes used for the cation with a lower charge, while the ending '-ic' is used for the cation with the higher charge. Example: Iron has two stable cation forms: Fe(II) and Fe(III). In this case, Fe(II) can be named as ferrous (with the ending '-ous' to indicate the lower charge) and Fe(III) as ferric (with the ending '-ic' for the higher charge).

Key concepts

Stock System

Understanding the Stock system is crucial for accurately naming compounds in chemistry, particularly for elements that can form more than one type of cation. In such cases, standardized rules apply to convey precisely which ionic version of the element is present in a compound. This clarity is achieved through the use of Roman numerals.
For instance, consider cobalt which can exist as either Co(II) or Co(III). The Stock system helps us to differentiate these by naming them cobalt(II) and cobalt(III), respectively. Similarly, for copper, Cu(I) would be copper(I) and Cu(II) would be copper(II). The numeral conveys the oxidation state, indicating the cation's positive charge, and thus allows chemists to communicate intricate details about a compound's makeup without ambiguity.

Ionic Compounds

Ionic compounds are formed when atoms of metals and nonmetals exchange electrons, resulting in a compound composed of ions. These ions are electrically charged particles; metals tend to lose electrons and form positively charged ions called cations, while nonmetals tend to gain electrons and form negatively charged particles known as anions.
The crux of naming ionic compounds lies in understanding the charges involved. For instance, sodium chloride is made up of sodium ions (Na+) and chloride ions (Cl-). Each ion's charge must be considered when constructing the compound's formula. The overall charge of the compound is neutral because the total positive charge of the cations balances the total negative charge of the anions. This principle is the basis for determining the formulas of ionic compounds.

Cation Charges

The charge of a cation is a defining feature used in chemical nomenclature. Many transition metals can form cations with different charges, which significantly impacts the nomenclature process.
For example, iron can form cations with a charge of +2 or +3. These are named using either the Stock system or traditional names. In the Stock system, these would be iron(II) and iron(III), denoting the different charges. Traditional nomenclature uses the suffixes '-ous' and '-ic': iron with a +2 charge is called 'ferrous' and with a +3 charge, 'ferric'. Knowing the cation charges is vital for correctly naming compounds and for understanding their chemical properties and reactions.

Nomenclature Rules

Chemical nomenclature follows a set of rules for naming compounds that have been standardized internationally to ensure clear communication among scientists. The periodic table groups elements that often form similar charges in the same column, facilitating memorization of common ionic charges.

Rule for Ionic Compounds:

The name of the metal (cation) comes first, followed by the name of the nonmetal (anion), with its ending changed to '-ide'. If the metal can have multiple positive charges, the charge is indicated in parentheses immediately after the metal's name using the Stock system, or alternatively, with the '-ous' or '-ic' suffix for lower or higher charge respectively.
These rules do not just name the elements but also imply the substance's proportions based on the charges of the ions. By following these nomenclature standards, anyone in the scientific community can understand the exact composition of a compound solely by its name.