Question

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

Short answer

(a) CaO: Cation - Calcium ion (Ca) with a +2 charge; Anion - Oxide ion (O) with a -2 charge. (b) Na2SO4: Cation - Sodium ion (Na) with a +1 charge; Anion - Sulfate ion (SO4) with a -2 charge. (c) KClO4: Cation - Potassium ion (K) with a +1 charge; Anion - Perchlorate ion (ClO4) with a -1 charge. (d) Fe(NO3)2: Cation - Iron ion (Fe) with a +2 charge; Anion - Nitrate ion (NO3) with a -1 charge. (e) Cr(OH)3: Cation - Chromium ion (Cr) with a +3 charge; Anion - Hydroxide ion (OH) with a -1 charge.

Step-by-step solution

(a) Identifying the cation and anion in CaO

In CaO, the cation is the calcium ion (Ca) with a +2 charge, while the anion is the oxide ion (O) with a -2 charge.

(b) Identifying the cation and anion in Na2SO4

In Na2SO4, the cation is the sodium ion (Na) with a +1 charge. The anion is the sulfate ion (SO4) with a -2 charge.

(c) Identifying the cation and anion in KClO4

In KClO4, the cation is the potassium ion (K) with a +1 charge. The anion is the perchlorate ion (ClO4) with a -1 charge.

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

In Fe(NO3)2, the cation is the iron ion (Fe) with a +2 charge. The anion is the nitrate ion (NO3) with a -1 charge.

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

In Cr(OH)3, the cation is the chromium ion (Cr) with a +3 charge. The anion is the hydroxide ion (OH) with a -1 charge.

Key concepts

Cation and Anion Identification

Understanding the components of ionic compounds is crucial for naming them and predicting their properties. Ionic compounds consist of positive ions, known as cations, and negative ions, called anions.

To identify cations and anions in a compound, look for the metal elements and polyatomic ions in the case of complex anions. In the compound CaO, for example, calcium (Ca), a metal, is the cation, and it typically forms a charge of +2, denoted as Ca²⁺. Oxygen (O), on the other hand, is a nonmetal and forms the anion with a charge of -2, or O^2-.

Another example is Na₂SO₄, where sodium (Na), the cation, has a charge of +1. Sulfate (SO₄) is a polyatomic anion with a charge of -2. The charges are critical since they must balance out for the compound to be electrically neutral.

Chemical Formulas

The chemical formula of an ionic compound tells us the ratio of cations to anions that combine to form a neutral compound. It's like a recipe for atoms. The subscript numbers in chemical formulas indicate how many of each ion are needed to balance the charges.

For example, in KClO₄, there is one potassium ion (K⁺) and one perchlorate ion (ClO₄^-), thus no subscript is needed for a 1:1 ratio. However, in Fe(NO₃)₂, the subscript 2 indicates that two nitrate ions (NO₃^-) are required to balance the +2 charge of the iron ion (Fe²⁺).

Ionic Charges

Ion charges are the key to understanding the formation and composition of ionic compounds. Metals tend to lose electrons to achieve a stable electron configuration, forming positive ions or cations. Nonmetals tend to gain electrons, forming negative ions or anions.

The charge of an ion is determined by the number of electrons transferred. For instance, chromium (Cr) in Cr(OH)₃ achieves a stable arrangement by losing three electrons, which gives it a 3+ charge. Each hydroxide ion (OH^-) has gained one electron, leading to a 1- charge. The crux is that the sum of the charges in the formula must be zero, which is why you see three hydroxide ions for every one chromium ion.