Question

Name the following ionic compounds: (a) \(\mathrm{MgO}\), (b) \(\mathrm{AlCl}_{3}\), (c) \(\mathrm{Li}_{3} \mathrm{PO}_{4}\), (d) \(\mathrm{Ba}\left(\mathrm{ClO}_{4}\right)_{2}\), (e) \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\) (f) \(\mathrm{Fe}(\mathrm{OH})_{2},(\mathrm{~g}) \mathrm{Ca}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\), (h) \(\mathrm{Cr}_{2}\left(\mathrm{CO}_{3}\right)_{3}\), (i) \(\mathrm{K}_{2} \mathrm{CrO}_{4}\) (j) \(\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}\).

Short answer

(a) Magnesium Oxide, (b) Aluminum Chloride, (c) Lithium Phosphate, (d) Barium Perchlorate, (e) Copper(II) Nitrate, (f) Iron(II) Hydroxide, (g) Calcium Acetate, (h) Chromium(III) Carbonate, (i) Potassium Chromate, (j) Ammonium Sulfate.

Step-by-step solution

(a) MgO

The cation in this compound is Magnesium (Mg) and the anion is Oxygen(O). Oxygen forms oxide ions (O²⁻). Therefore, the compound is named Magnesium Oxide.

(b) AlCl3

The cation in this compound is Aluminum (Al) and the anion is Chlorine (Cl). Chlorine forms chloride ions (Cl⁻). Therefore, the compound is named Aluminum Chloride.

(c) Li3PO4

The cation is Lithium (Li) and the anion is made up of one Phosphorus (P) and four Oxygen (O) atoms, which is called a Phosphate ion (\(PO_4^{3-}\)). Therefore, the compound is named Lithium Phosphate.

(d) Ba(ClO4)2

The cation in this compound is Barium (Ba) and the anion is made up of Chlorine (Cl) and four Oxygen (O) atoms, which is called a Perchlorate ion (\(ClO_4^-\)). Therefore, the compound is named Barium Perchlorate.

(e) Cu(NO3)2

The cation in this compound is Copper (Cu). Since this is a transition metal, we need to use Roman numerals to indicate its charge. Here, Copper's charge is 2+ because it is paired with two nitrate ions (\(NO_3^-\)). The anion is made up of one Nitrogen (N) and three Oxygen (O) atoms, called a Nitrate ion (\(NO_3^-\)). Therefore, this compound is named Copper(II) Nitrate.

(f) Fe(OH)2

The cation is Iron (Fe) and it's a transition metal as well. In this case, its charge is 2+. The anion is made up of Oxygen (O) and Hydrogen (H) atoms, called Hydroxide ions (\(OH^-\)). Therefore, the compound is named Iron(II) Hydroxide.

(g) Ca(C2H3O2)2

The cation in this compound is Calcium (Ca), and the anion is made up of two Carbon (C), three Hydrogen (H), and two Oxygen (O) atoms, called an Acetate ion (\(C_2H_3O_2^-\)). The compound is named Calcium Acetate.

(h) Cr2(CO3)3

The cation in this compound is Chromium (Cr), which is another transition metal, having a charge of 3+ in this case. The anion is made up of one Carbon (C) and three Oxygen (O) atoms, called a Carbonate ion (\(CO_3^{2-}\)). Therefore, the compound is named Chromium(III) Carbonate.

(i) K2CrO4

The cation in this compound is Potassium (K) and the anion is made up of one Chromium (Cr) and four Oxygen (O) atoms, called a Chromate ion (\(CrO_4^{2-}\)). Thus, the compound is named Potassium Chromate.

(j) (NH4)2SO4

The cation in this compound is made up of one Nitrogen (N) and four Hydrogen (H) atoms, called an Ammonium ion (\(NH_4^+\)). The anion is made up of one Sulfur (S) and four Oxygen (O) atoms, called a Sulfate ion (\(SO_4^{2-}\)). Therefore, the compound is named Ammonium Sulfate.

Key concepts

Cation and Anion Identification

When naming ionic compounds, it is important to first identify the cations and anions involved. A cation is a positively charged ion, usually a metal, that has lost one or more electrons. For example, the magnesium ion ( Mg^{2+} ) in MgO or the aluminum ion ( Al^{3+} ) in AlCl_3 . An anion, on the other hand, is a negatively charged ion, usually a non-metal, that has gained one or more electrons. For instance, the oxide ion ( O^{2-} ) paired with magnesium in MgO or the chloride ion ( Cl^- ) in AlCl_3 . The correct identification of these ions is crucial since it guides the naming process of the compound based on the ions it contains.

Nomenclature of Ionic Compounds

Naming ionic compounds involves a systematic approach that starts with the cation followed by the anion. For simple ionic compounds, you directly name the metal followed by the non-metal with an 'ide' suffix for the anion. Some examples include magnesium oxide for MgO and aluminum chloride for AlCl_3 . Here are key steps for naming ionic compounds:

• Write the cation name (metal).
• Write the anion name, changing the ending to 'ide' if it is a simple ion.
• If the ion is polyatomic, use the name of the polyatomic ion directly.

This nomenclature provides precise communication in chemistry, allowing chemists to understand the composition of compounds.

Transition Metals with Roman Numerals

For ionic compounds that include transition metals, Roman numerals indicate the charge of the metal ion. This is essential because many transition metals can have multiple oxidation states. For example, copper in Cu(NO_3)_2 is denoted as Copper(II) because the copper ion forms a 2+ charge when it pairs with two nitrate ions ( NO_3^- ). Key considerations for naming such compounds include:

• Identify the charge on the transition metal by balancing it with the total negative charge of the anion.
• Use Roman numerals in the name to denote the metal's charge, e.g., Iron(II) hydroxide for Fe(OH)_2 .

This system of using Roman numerals helps to distinguish between the different ionic forms that transition metals can adopt.

Polyatomic Ions Naming

Polyatomic ions are ions composed of two or more atoms covalently bonded, that carry a charge. Naming compounds involving polyatomic ions involves using the ion's name directly. For instance, sulfate ( SO_4^{2-} ) in ( NH_4)_2SO_4 or phosphate ( PO_4^{3-} ) in Li_3PO_4 . Some common polyatomic ions and their naming conventions include:

• Nitrate NO_3^-
• Hydroxide OH^-
• Acetate C_2H_3O_2^-

When naming ionic compounds with polyatomic ions, simply combine the cation name with the full polyatomic ion name. This retains clarity and consistency in chemical nomenclature. It ensures that the complex ion structures are appropriately acknowledged in the compound's full name.