Question

Give the names and charges of the cation and anion in each of the following compounds: (a) CuS, (b) ${\mathrm{Ag}}_2{\mathrm{SO}}_4$, (c) $\mathrm{Al}{\left({\mathrm{ClO}}_3\right)}_3$ (d) $\mathrm{Co}(\mathrm{OH}{)}_2$ (e) ${\mathrm{PbCO}}_3$

Short answer

(a) Copper (II) cation, +2 charge; Sulfide anion, -2 charge. (b) Silver cation, +1 charge; Sulfate anion, -2 charge. (c) Aluminum cation, +3 charge; Chlorate anion, -1 charge. (d) Cobalt (II) cation, +2 charge; Hydroxide anion, -1 charge. (e) Lead (II) cation, +2 charge; Carbonate anion, -2 charge.

Step-by-step solution

Identify the cations and anions

For each compound, we will start by identifying the cation, which is typically the positively charged element or polyatomic ion in the compound, and the anion, the negatively charged element or polyatomic ion. (a) CuS: The cation is Cu (copper) and the anion is S (sulfur). (b) ${\mathrm{Ag}}_2{\mathrm{SO}}_4$: The cation is Ag (silver) and the anion is ${\mathrm{SO}}_4$ (sulfate). (c) $\mathrm{Al}({\mathrm{ClO}}_3{)}_3$: The cation is Al (aluminum) and the anion is ${\mathrm{ClO}}_3$ (chlorate). (d) $\mathrm{Co}(\mathrm{OH}{)}_2$: The cation is Co (cobalt) and the anion is $\mathrm{OH}$ (hydroxide). (e) ${\mathrm{PbCO}}_3$: The cation is Pb (lead) and the anion is ${\mathrm{CO}}_3$ (carbonate).

Determine the charges of the cations and anions

Now that we have identified the cations and anions, we need to determine their charges. We can use the periodic table or our knowledge of the common charges of elements and polyatomic ions. (a) CuS: Cu is a transition metal and can have different charges. Since sulfur typically forms a charge of -2, Cu would have a charge of +2. Sulfur has a charge of -2. (b) ${\mathrm{Ag}}_2{\mathrm{SO}}_4$: Silver (Ag) has a charge of +1 and sulfate (${\mathrm{SO}}_4$) has a charge of -2. (c) $\mathrm{Al}({\mathrm{ClO}}_3{)}_3$: Aluminum (Al) has a charge of +3 and chlorate (${\mathrm{ClO}}_3$) has a charge of -1. (d) $\mathrm{Co}(\mathrm{OH}{)}_2$: Cobalt (Co) is a transition metal and can have different charges. Since hydroxide (OH) has a charge of -1, Co would have a charge of +2. Hydroxide has a charge of -1. (e) ${\mathrm{PbCO}}_3$: Lead (Pb) is also a transition metal and can have different charges. Since carbonate (${\mathrm{CO}}_3$) has a charge of -2, Pb would have a charge of +2.

Give the names and charges of the cations and anions

Finally, we will provide the names and charges of the cations and anions. (a) CuS: The cation is Copper (II) with a charge of +2; the anion is Sulfide with a charge of -2. (b) ${\mathrm{Ag}}_2{\mathrm{SO}}_4$: The cation is Silver with a charge of +1; the anion is Sulfate with a charge of -2. (c) $\mathrm{Al}({\mathrm{ClO}}_3{)}_3$: The cation is Aluminum with a charge of +3; the anion is Chlorate with a charge of -1. (d) $\mathrm{Co}(\mathrm{OH}{)}_2$: The cation is Cobalt (II) with a charge of +2; the anion is Hydroxide with a charge of -1. (e) ${\mathrm{PbCO}}_3$: The cation is Lead (II) with a charge of +2; the anion is Carbonate with a charge of -2.

Key concepts

Cations and Anions

In ionic compounds, it's crucial to identify which parts are cations and which are anions. Cations are positively charged ions, whereas anions are negatively charged ions.

To clearly pick these out in compounds, remember:

• The cation is usually a metal element and takes up the positive charge. Metals, by nature, lose electrons, resulting in a positive charge.
• The anion is typically a non-metal or a group of atoms, like polyatomic ions, carrying a negative charge. Non-metals tend to gain electrons, thus having a negative charge.

For example, in CuS, copper (Cu) is the cation due to its metallic nature, and sulfur (S) becomes the anion. Each plays a vital role in keeping the compound stable.

Chemical Charges

Understanding the charges in chemical compounds is essential. Chemical charges result from the losing or gaining of electrons, leading an element to become either a cation or an anion.

The fundamental principle is straightforward: a cation has a positive charge because it has lost one or more electrons. Conversely, an anion possesses a negative charge, having gained electrons.

• Transition metals, such as copper or lead, can have multiple charges. This is why we often see notations like Copper (II) in a compound.
• Main group metals commonly have a consistent charge. Alkali metals (like lithium) usually have a +1 charge, while alkaline earth metals (like magnesium) have a +2 charge.
• Non-metals, such as chlorine or sulfur, accept electrons and commonly bear a negative charge.
• Polyatomic ions also have specific charges, like sulfate (${\mathrm{SO}}_4^{2-}$) or hydroxide (${\mathrm{OH}}^{-}$).

Mastering these common charges can significantly ease the process of working with chemical formulas.

Identifying Ionic Compounds

Ionic compounds consist of a mixture of cations and anions. These combinations form strong ionic bonds, which occur due to electrostatic attraction between opposite charges. Recognizing ionic compounds in chemical equations helps understand their properties.

Generally, any compound formed from metals and non-metals is likely ionic.
To identify these compounds:

• Look for compounds with a metal as the first element (denotes a likely cation).
• Check if there are any recognized polyatomic ions present, as they often indicate ionic nature.
• Consider the overall charge balance; the sum of the charges should be zero, which confirms all ions are correctly paired within the compound.

The clarity of ionic narratives in compounds like ${\mathrm{Ag}}_2{\mathrm{SO}}_4$ or $\mathrm{Al}{\left({\mathrm{ClO}}_3\right)}_3$ stems from this systematic approach.

Polyatomic Ions

Polyatomic ions are groups of atoms that behave as a single charged unit. Unlike monatomic ions, polyatomic ions comprise several atoms bonded together, carrying an overall charge.

Some common polyatomic ions include:

• Sulfate (${\mathrm{SO}}_4^{2-}$) - a frequent anion found in many compounds.
• Nitrate (${\mathrm{NO}}_3^{-}$) and chlorate (${\mathrm{ClO}}_3^{-}$) have a single negative charge, and are present in various chemical reactions.
• Hydroxide (${\mathrm{OH}}^{-}$) is another polyatomic ion, often bonded with metals.
• Carbonate (${\mathrm{CO}}_3^{2-}$) regularly appears in chemistry, as seen in compounds like ${\mathrm{PbCO}}_3$.

Remembering these key ions, along with their charges, is indispensable for anyone studying chemistry, as they frequently appear in both academic settings and practical applications.