Question

The names given for the following compounds are incorrect. Write the correct name for each compound. (a) \(\mathrm{Cu}_{3} \mathrm{PO}_{4},\) copper(III) phosphate (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), sodium sulfide (c) \(\mathrm{MnO}_{2}\), manganese(II) oxide (d) \(\mathrm{AuCl}_{3},\) gold chloride (e) \(\mathrm{Pb}\left(\mathrm{CO}_{3}\right)_{2}\), lead(II) acetate (f) \(\mathrm{Ni}_{2} \mathrm{~S}_{3},\) nickel(II) sulfide

Short answer

(a) Copper(I) phosphate, (b) Sodium sulfate, (c) Manganese(IV) oxide, (d) Gold(III) chloride, (e) Lead(IV) carbonate, (f) Nickel(III) sulfide.

Step-by-step solution

Analyze the first compound

The chemical formula is \(\mathrm{Cu}_3\mathrm{PO}_4\). Copper typically has oxidation states of +1 or +2. For \(\mathrm{PO}_4^{3-}\) (phosphate), the phosphate ion carries a -3 charge. To balance, we need three \(\mathrm{Cu}^+\) ions: \((+1 \times 3 = +3)\), to match the -3 of phosphate. Therefore, the correct name is "copper(I) phosphate," not "copper(III) phosphate."

Analyze the second compound

The chemical formula is \(\mathrm{Na}_2\mathrm{SO}_4\). \(\mathrm{Na}\) is sodium, and \(\mathrm{SO}_4^{2-}\) is sulfate, not sulfide. Sodium ions are \(\mathrm{Na}^+\), with a +1 charge, and the sulfate ion is \(\mathrm{SO}_4^{2-}\) with a -2 charge. Thus, two sodium ions are needed to balance one sulfate ion, resulting in the correct name "sodium sulfate."

Analyze the third compound

The compound is \(\mathrm{MnO}_2\). \(\mathrm{O}\) (oxide) has a -2 oxidation state. To balance two \(\mathrm{O}^{2-}\) ions (-2 each for a total of -4), \(\mathrm{Mn}\) must be +4, not +2. Hence, the correct name is "manganese(IV) oxide," rather than "manganese(II) oxide."

Analyze the fourth compound

The compound is \(\mathrm{AuCl}_3\). \(\mathrm{Cl}\) has a -1 charge, and with three \(\mathrm{Cl}^-\) ions, the total is -3. Therefore, gold must be in the +3 oxidation state to balance, so the correct name is "gold(III) chloride," instead of "gold chloride."

Analyze the fifth compound

The compound is \(\mathrm{Pb}(\mathrm{CO}_3)_2\). Each \(\mathrm{CO}_3^{2-}\) ion (carbonate) carries a -2 charge, for a total of -4. Thus, lead must be +4. Therefore, the correct name is "lead(IV) carbonate," not "lead(II) acetate."

Analyze the sixth compound

The compound is \(\mathrm{Ni}_2 \mathrm{S}_3\). Sulfur \((\mathrm{S})\) typically has a -2 charge. Here we have three sulfide ions \((-2 \times 3 = -6)\). To balance, two nickel ions must have a total charge of +6, so each must be +3. Thus, the correct name is "nickel(III) sulfide," instead of "nickel(II) sulfide."

Key concepts

Oxidation States

When dealing with inorganic compounds, understanding oxidation states is crucial for correctly identifying chemical names and formulas. The oxidation state of an element is essentially the charge it would have if all the bonds in the compound were ionic. Transition metals, like copper and manganese, often have multiple possible oxidation states due to their electron configurations.
For instance, copper can exist in either a +1 or a +2 oxidation state. The compound \(\mathrm{Cu}_3 \mathrm{PO}_4\) requires copper to be in a +1 state to balance the charge of the phosphate ion \((\mathrm{PO}_4^{3-})\), leading to the correct name "copper(I) phosphate."
When naming compounds, it's essential to determine the correct oxidation state of the metal involved by using the charges of the other elements or groups in the formula. This process helps in accurately writing and understanding chemical names.

Ionic Compounds

Ionic compounds are composed of positively charged ions, called cations, and negatively charged ions, called anions. Metals typically form cations while nonmetals form anions. In compounds like \(\mathrm{Na}_2 \mathrm{SO}_4\), sodium ions \((\mathrm{Na}^+)\) pair with the sulfate ion \((\mathrm{SO}_4^{2-})\) to create a balanced ionic compound.
The electrostatic attraction between the two types of ions holds the compound together, which is a hallmark of ionic compounds. Through this interaction, the resulting compound achieves electrical neutrality.
Correctly naming ionic compounds involves identifying the ions and their charges, then aligning them to ensure that the net charge is zero. This forms the basis for naming compounds such as "sodium sulfate," rather than "sodium sulfide," in this example.

Chemical Formulas

Chemical formulas provide a concise way of representing the elements in a compound and their respective quantities. Each element's symbol is usually accompanied by a number, indicating the number of atoms of each element in one unit of the compound.
Understanding chemical formulas requires recognizing how subscripts in a formula indicate the ratio of ions or elements. Take, for instance, \(\mathrm{AuCl}_3\), where three chloride ions \((\mathrm{Cl}^-)\) pair with one gold ion. The formula reflects the requirement for gold to be in the +3 oxidation state, making the compound gold(III) chloride.
Proper interpretation of chemical formulas is fundamental to writing the correct name of the compound, reflecting the correct stoichiometry and oxidation states of elements involved.

Transition Metals

Transition metals, such as iron and nickel, are distinguished by their ability to have variable oxidation states. This property arises because the d-electrons in transition metals are close in energy to the s-electrons.This capability of exhibiting multiple oxidation states makes it a bit tricky when naming their compounds. For example, nickel in \(\mathrm{Ni}_2 \mathrm{S}_3\) must have a +3 oxidation state to balance the -6 from three sulfur ions, thus named nickel(III) sulfide.
The transition metals' diverse oxidation states allow them to form colorful compounds and act as catalysts in chemical reactions. When learning about these metals, one must pay meticulous attention to the oxidation numbers to ensure accuracy in both writing and naming their chemical formulas.