Question

What is a polyatomic ion? Give examples of five common polyatomic ions.

Short answer

A polyatomic ion is a charged species composed of two or more atoms covalently bonded together or of a metal complex that acts as a single unit, carrying an overall net electrical charge. Five common polyatomic ions include: 1. Ammonium: \(\mathrm{NH}_4^+\) 2. Sulfate: \(\mathrm{SO}_4^{2-}\) 3. Nitrate: \(\mathrm{NO}_3^{-}\) 4. Hydroxide: \(\mathrm{OH}^{-}\) 5. Carbonate: \(\mathrm{CO}_3^{2-}\)

Step-by-step solution

Define polyatomic ion

A polyatomic ion is a charged species composed of two or more atoms covalently bonded together or of a metal complex that acts as a single unit. It carries an overall net electrical charge.

List five common polyatomic ions

Here are five common polyatomic ions, along with their chemical formulas and charges: 1. Ammonium: \(\mathrm{NH}_4^+\) 2. Sulfate: \(\mathrm{SO}_4^{2-}\) 3. Nitrate: \(\mathrm{NO}_3^{-}\) 4. Hydroxide: \(\mathrm{OH}^{-}\) 5. Carbonate: \(\mathrm{CO}_3^{2-}\)

Briefly explain each polyatomic ion

1. Ammonium (\(\mathrm{NH}_4^+\)): This ion consists of a nitrogen atom covalently bonded to four hydrogen atoms with a net positive charge. It is commonly found in salts such as ammonium chloride (\(\mathrm{NH}_4\mathrm{Cl}\)) and ammonium sulfate (\(\mathrm{(NH}_4\mathrm{)}_2\mathrm{SO}_4\)). 2. Sulfate (\(\mathrm{SO}_4^{2-}\)): This ion consists of a sulfur atom covalently bonded to four oxygen atoms with a net negative charge of 2. It is commonly found in salts like sodium sulfate (\(\mathrm{Na}_2\mathrm{SO}_4\)) and calcium sulfate (\(\mathrm{CaSO}_4\)). 3. Nitrate (\(\mathrm{NO}_3^{-}\)): This ion consists of a nitrogen atom covalently bonded to three oxygen atoms with a net negative charge. It is commonly found in salts like potassium nitrate (\(\mathrm{KNO}_3\)) and silver nitrate (\(\mathrm{AgNO}_3\)). 4. Hydroxide (\(\mathrm{OH}^{-}\)): This ion consists of an oxygen atom covalently bonded to a hydrogen atom with a net negative charge. It is commonly found in bases like sodium hydroxide (\(\mathrm{NaOH}\)) and potassium hydroxide (\(\mathrm{KOH}\)). 5. Carbonate (\(\mathrm{CO}_3^{2-}\)): This ion consists of a carbon atom covalently bonded to three oxygen atoms with a net negative charge of 2. It is commonly found in salts like calcium carbonate (\(\mathrm{CaCO}_3\)) and sodium carbonate (\(\mathrm{Na}_2\mathrm{CO}_3\)).

Key concepts

Ammonium Ion

The ammonium ion is a fascinating example of a positively charged polyatomic ion. It is composed of one nitrogen atom bonded to four hydrogen atoms, forming the chemical formula \( \mathrm{NH}_4^+ \). The overall positive charge results from the nitrogen atom accommodating an extra proton.
This ion is commonly found in ammonia derivatives and fertilizers, due to its ability to easily dissolve in water and provide essential nutrients. Examples of such compounds include ammonium chloride (\( \mathrm{NH}_4\mathrm{Cl} \)) and ammonium sulfate (\( \mathrm{(NH}_4\mathrm{)}_2\mathrm{SO}_4 \)).

• Provides nitrogen to plants
• Used in household cleaners
• Participates in acid-base reactions

Sulfate Ion

Sulfate ions are important components of many substances and they are prevalent in the environment. This ion is comprised of a sulfur atom surrounded by four oxygen atoms, resulting in the chemical formula \( \mathrm{SO}_4^{2-} \). This configuration carries a 2- charge because two more electrons are present than protons.
Sulfates are found in numerous minerals and are often used in industrial applications, such as in the production of gypsum for plaster or wallboard. Common forms include sodium sulfate (\( \mathrm{Na}_2\mathrm{SO}_4 \)) and calcium sulfate (\( \mathrm{CaSO}_4 \)).

• Used in detergents and glass production
• Occurs naturally in mineral deposits
• Forms precipitation as rain or snow

Nitrate Ion

The nitrate ion, another essential polyatomic ion, consists of one nitrogen atom bonded to three oxygen atoms, expressed as \( \mathrm{NO}_3^{-} \). The negative charge occurs because there is one more electron than there are protons in the structure.
Nitrates play a crucial role in the nitrogen cycle and are key to plant growth. They are commonly found in compounds such as potassium nitrate (\( \mathrm{KNO}_3 \)) and silver nitrate (\( \mathrm{AgNO}_3 \)).

• Key component of fertilizers
• Found in explosives such as gunpowder
• Used in food preservation

Hydroxide Ion

The hydroxide ion is a simple but significant polyatomic ion composed of one oxygen atom bonded to a hydrogen atom, shown as \( \mathrm{OH}^{-} \). The negative charge is due to the presence of an additional electron.
Found commonly in bases, hydroxides contribute to the alkaline properties of compounds. Familiar examples are sodium hydroxide (\( \mathrm{NaOH} \)) and potassium hydroxide (\( \mathrm{KOH} \)).

• Used in chemical synthesis
• Essential for saponification in soap production
• Neutralizes acids, increasing pH

Carbonate Ion

The carbonate ion features a central carbon atom surrounded by three oxygen atoms, with the chemical formula \( \mathrm{CO}_3^{2-} \). Its 2- charge is due to two extra electrons in the atomic structure.
Carbonates are pivotal in geology and biology, forming essential parts of shells and skeletons in marine organisms. They are found in compounds like calcium carbonate (\( \mathrm{CaCO}_3 \)) and sodium carbonate (\( \mathrm{Na}_2\mathrm{CO}_3 \)).

• Key component of limestone
• Used for water softening
• Acts as a buffering agent in chemistry