Question

In each of the following, identify which names are incorrect for the given formulas, and give the correct name. a. \(\mathrm{CaH}_{2}\), calcium hydride b. \(\mathrm{PbCl}_{2}\), lead(IV) chloride c. \(\mathrm{CrI}_{3}\), chromium(III) iodide d. \(\mathrm{Na}_{2} \mathrm{~S}\), disodium sulfide e. \(\mathrm{CuBr}_{2}\), cupric bromide

Short answer

The incorrect names and their correct versions are: b. lead(IV) chloride → lead(II) chloride d. disodium sulfide → sodium sulfide For the other compounds, their provided names are correct: a. calcium hydride c. chromium(III) iodide e. cupric bromide (or copper(II) bromide)

Step-by-step solution

a. Analyzing Calcium Hydride

The given formula is \(\mathrm{CaH}_{2}\). Calcium (Ca) has a +2 charge, and hydrogen (H) has a -1 charge. There are 2 hydrogen atoms to balance the charge, making the formula correct. The name "calcium hydride" is also accurate.

b. Analyzing Lead(IV) Chloride

The given formula is \(\mathrm{PbCl}_{2}\). Lead (Pb) is a transition metal, and in this case, it has a +2 charge (as indicated by the subscript for chlorine). Chlorine (Cl) has a -1 charge. However, the name states lead(IV) chloride, which would indicate a +4 charge for lead. So, the correct name for this formula should be lead(II) chloride.

c. Analyzing Chromium(III) Iodide

The given formula is \(\mathrm{CrI}_{3}\). Chromium (Cr) has a +3 charge (as indicated by the Roman numeral in parentheses) and iodine (I) has a -1 charge. There are 3 iodine atoms to balance the charge, making both the formula and the given name "chromium(III) iodide" correct.

d. Analyzing Disodium Sulfide

The given formula is \(\mathrm{Na}_{2} \mathrm{~S}\). Sodium (Na) has a +1 charge and sulfur (S) has a -2 charge. There are 2 sodium atoms to balance the charge. The given name is "disodium sulfide," which is incorrect. The correct name should be simply sodium sulfide.

e. Analyzing Cupric Bromide

The given formula is \(\mathrm{CuBr}_{2}\). Copper (Cu) is a transition metal, and in this case, it has a +2 charge (as indicated by the subscript for bromine). Bromine (Br) has a -1 charge. The name "cupric bromide" is an older naming convention, and it is correct. However, the modern IUPAC name would be copper(II) bromide. So, both cupric bromide and copper(II) bromide are considered correct names for this compound.

Key concepts

Ionic Compounds

Ionic compounds are formed when positive and negative ions attract each other. These ions are usually metals and non-metals. For instance, in the compound \( \mathrm{CaH}_{2} \), calcium is a metal with a +2 charge, while each hydrogen has a -1 charge. The opposite charges cause the ions to bond together, creating a stable ionic compound. Ionic compounds generally appear as neutral compounds, which means the total positive charge must balance the total negative charge.

• Metals lose electrons to become positively charged ions.
• Non-metals gain electrons to become negatively charged ions.
• Ionic compounds have high melting and boiling points.

This behavior is evident in compounds like \( \mathrm{Na}_{2} \mathrm{~S} \), where two sodium ions balance the charge of a single sulfide ion. Understanding how ions combine gives insight into naming ionic compounds correctly.

Transition Metals

Transition metals are found in the middle block of the periodic table. These metals are unique because they can form more than one type of charged ion. This characteristic complicates the nomenclature of compounds containing these metals. For example, lead and copper, as seen in the compounds \( \mathrm{PbCl}_{2} \) and \( \mathrm{CuBr}_{2} \), are transition metals.

• Transition metals can form multiple oxidation states.
• This property affects how we name compounds they form.

Often, Roman numerals indicate the charge of transition metals in compound names. However, in older naming conventions, suffixes such as '-ic' and '-ous' were used to denote higher and lower charges, respectively, like cupric and cuprous for copper.

Oxidation States

Oxidation states represent the charge of an element's ion. In ionic compounds, it's crucial to know these charges to determine the correct formula or name. For transition metals, like chromium in \( \mathrm{CrI}_{3} \), specifying the oxidation state in the name helps clarify the compound's composition.

• The oxidation state is shown with Roman numerals in parentheses.
• It helps identify how many electrons an atom has gained or lost.
• Correctly naming transition metal compounds provides accurate chemical understanding.

For example, lead in \( \mathrm{PbCl}_{2} \) is +2, not +4 as the incorrect name "lead(IV) chloride" suggests. Identifying the proper oxidation state ensures that the compound's name reflects the true structure.

IUPAC Naming System

The IUPAC naming system is a standardized way to name chemical compounds. This system ensures that each compound has a unique and universally recognised name. When naming ionic compounds, especially those involving transition metals, the IUPAC system provides clarity. For instance, \( \mathrm{CuBr}_{2} \) is named "copper(II) bromide" in accordance with IUPAC guidelines, highlighting the copper ion's +2 charge.

• IUPAC names prevent ambiguity in chemical nomenclature.
• Roman numerals denote the charge of transition metal ions.
• Provides consistency across the scientific community.

Older names, such as "cupric bromide," are replaced by IUPAC names to maintain global uniformity. Practicing IUPAC naming supports effective communication in chemistry and avoids confusion.