Question

Give the names and charges of the cation and anion each of the following compounds: (a) \(\mathrm{CaO}\), (b) \(\mathrm{Na}_{2} \mathrm{SO}\) (c) \(\mathrm{KClO}_{4}\), (d) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}\), (e) \(\mathrm{Cr}(\mathrm{OH})_{3}\).

Short answer

(a) Cation: Calcium (Ca), Charge: +2, Anion: Oxygen (O), Charge: -2; (b) Cation: Sodium (Na), Charge: +1, Anion: SO, Charge: -2; (c) Cation: Potassium (K), Charge: +1, Anion: ClO4, Charge: -1; (d) Cation: Iron (Fe), Charge: +2, Anion: NO3, Charge: -1; (e) Cation: Chromium (Cr), Charge: +3, Anion: OH, Charge: -1.

Step-by-step solution

(a) Identifying cation and anion in CaO

In the compound CaO, the elements are calcium (Ca) and oxygen (O). Calcium is a metal and forms a cation while oxygen is a non-metal and forms an anion. The charges of these ions can be found from the periodic table. Calcium has a charge of +2 and the oxygen has a charge of -2, making the compound electrically neutral. Cation: Calcium (Ca), Charge: +2 Anion: Oxygen (O), Charge: -2

(b) Identifying cation and anion in Na2SO

In the compound Na2SO, the elements are sodium (Na) and sulfur (S) together with oxygen (O). Sodium forms a cation, while sulfur and oxygen together form the SO anion. Sodium has a charge of +1, and since there are two sodium ions, we have a total positive charge of +2. For the SO anion, we know that oxygen has a charge of -2 and we need a +2 charge on sulfur to balance the charge. Therefore, Cation: Sodium (Na), Charge: +1 Anion: SO, Charge: -2

(c) Identifying cation and anion in KClO4

In the compound KClO4, the elements are potassium (K), chlorine (Cl), and oxygen (O). Potassium forms a cation while chlorine and oxygen together form the ClO4 anion. Potassium has a charge of +1 and, since the compound must be electrically neutral, the ClO4 anion must have a charge of -1. So, Cation: Potassium (K), Charge: +1 Anion: ClO4, Charge: -1

(d) Identifying cation and anion in Fe(NO3)2

In the compound Fe(NO3)2, the elements are iron (Fe), nitrogen (N), and oxygen (O). Iron forms a cation, while the NO3 group forms an anion. From the compound, we can see that there are 2 NO3 groups, each with a charge of -1, making the total negative charge -2. Since the compound is neutral, the iron cation must have a charge of +2. Thus, Cation: Iron (Fe), Charge: +2 Anion: NO3, Charge: -1

(e) Identifying cation and anion in Cr(OH)3

In the compound Cr(OH)3, the elements are chromium (Cr), oxygen (O), and hydrogen (H). Chromium forms a cation while the OH group forms an anion. From the compound, we can see that there are 3 OH groups, each with a charge of -1, making the total negative charge -3. Since the compound is neutral, the chromium cation must have a charge of +3. Therefore, Cation: Chromium (Cr), Charge: +3 Anion: OH, Charge: -1

Key concepts

Cation and Anion Identification

Understanding ionic compounds begins with identifying cations and anions, the positively and negatively charged ions that make up these compounds. A cation, typically a metal, loses electrons and carries a positive charge, while an anion, often a non-metal or a polyatomic ion, gains electrons and carries a negative charge. For example, in calcium oxide (CaO), calcium (Ca) is the cation with a +2 charge, and oxygen (O) is the anion with a -2 charge. The sum of charges in a stable ionic compound is always zero, reflecting a balance between the positive and negative ions.

When identifying these ions in a compound, you would look for the metal element to indicate the cation, and the non-metal or polyatomic ion for the anion. For instance, in potassium perchlorate (KClO₄), potassium (K) is the cation with a +1 charge, and the perchlorate ion (ClO₄) is the anion with a -1 charge. The simplicity of identifying cations and anions lies in recognizing the patterns of ionic charges on the periodic table and applying this to determining the composition of the compound.

Chemical Compound Nomenclature

The naming of chemical compounds, or nomenclature, follows specific rules that allow scientists to communicate without ambiguity. Ionic compounds are named with the cation first followed by the anion. When naming a compound, the cation retains the element name, such as sodium in sodium sulfate, while the anion changes its suffix. For instance, the anion of chlorine becomes chloride, as in sodium chloride.

For polyatomic ions, common names are often used, like sulfate for SO₄^2- or nitrate for NO₃^-. Transition metal cations that can have more than one possible charge are indicated with Roman numerals in parentheses. For example, iron(II) nitrate specifies a +2 charge on the iron cation (Fe²⁺). It's important to become familiar with both the systematic names of ions and their common names to correctly name ionic compounds.

Periodic Table Charge Determination

The periodic table is a powerful tool for predicting the charges of ions in ionic compounds. Elements in the same group often form ions with the same charge due to their similar electron configurations. Group 1 elements, like sodium and potassium, typically form cations with a +1 charge, while Group 2 elements, such as calcium and magnesium, form +2 cations.

The charge of anions can also be anticipated based on their position on the periodic table. Non-metals in Group 17, like chlorine and bromine, usually form -1 anions, while oxygen and sulfur in Group 16 typically form -2 anions. For transition metals, such as iron or chromium, the charges can vary and are often determined by the context of the compound they are part of. Learning how to use the periodic table to predict ionic charges is vital for understanding and mastering the composition of ionic compounds.