Problem 8 - Chemistry and Chemical Reactivity

Question

Give the symbol, including the correct charge, for each of the following ions: (a) permanganate ion (b) nitrite ion (c) dihydrogen phosphate ion (d) ammonium ion (e) phosphate ion (f) sulfite ion

Step-by-Step Solution

Answer

(a) \( \text{MnO}_4^- \), (b) \( \text{NO}_2^- \), (c) \( \text{H}_2\text{PO}_4^- \), (d) \( \text{NH}_4^+ \), (e) \( \text{PO}_4^{3-} \), (f) \( \text{SO}_3^{2-} \).

Step 1: Identifying the Permanganate Ion Symbol

The permanganate ion is a polyatomic ion with the formula \( \text{MnO}_4^- \). It carries a -1 charge.

Step 2: Identifying the Nitrite Ion Symbol

The nitrite ion is a polyatomic ion with the formula \( \text{NO}_2^- \). It carries a -1 charge.

Step 3: Identifying the Dihydrogen Phosphate Ion Symbol

The dihydrogen phosphate ion is a polyatomic ion with the formula \( \text{H}_2\text{PO}_4^- \). It carries a -1 charge.

Step 4: Identifying the Ammonium Ion Symbol

The ammonium ion is a polyatomic ion with the formula \( \text{NH}_4^+ \). It carries a +1 charge.

Step 5: Identifying the Phosphate Ion Symbol

The phosphate ion is a polyatomic ion with the formula \( \text{PO}_4^{3-} \). It carries a -3 charge.

Step 6: Identifying the Sulfite Ion Symbol

The sulfite ion is a polyatomic ion with the formula \( \text{SO}_3^{2-} \). It carries a -2 charge.

Key Concepts

Polyatomic Ions

Polyatomic ions are ions that consist of more than one atom. Unlike monatomic ions, which are composed of a single atom, polyatomic ions contain multiple atoms that are covalently bonded together, sharing electrons.
Despite being made up of several atoms, polyatomic ions act as a single entity in chemical reactions. They carry a net charge, which can be positive or negative.
Common examples of polyatomic ions include:

• Permanganate ion - \( \text{MnO}_4^- \)
• Nitrite ion - \( \text{NO}_2^- \)
• Dihydrogen phosphate ion - \( \text{H}_2\text{PO}_4^- \)
• Ammonium ion - \( \text{NH}_4^+ \)
• Phosphate ion - \( \text{PO}_4^{3-} \)
• Sulfite ion - \( \text{SO}_3^{2-} \)

Each of these ions carries a specific charge, which plays a crucial role in forming chemical compounds.

Chemical Formulas

Chemical formulas are symbolic representations of compounds and ions. They show the types and numbers of atoms present in a molecule or ion. For example, the chemical formula for water, \( \text{H}_2\text{O} \), indicates that it contains two hydrogen atoms and one oxygen atom.
In the case of polyatomic ions, chemical formulas also reflect their composition and charge. For instance:

• \( \text{MnO}_4^- \) for permanganate ion shows one manganese atom bonded with four oxygen atoms.
• \( \text{NO}_2^- \) for nitrite ion illustrates one nitrogen atom bonded with two oxygen atoms.
• \( \text{NH}_4^+ \) for ammonium ion indicates one nitrogen atom bonded to four hydrogen atoms.

These formulas are essential for understanding how ions combine to form chemical compounds.

Charges of Ions

The charge of an ion is a key characteristic that determines how it interacts with other ions and elements. Ions can possess a positive charge (cation) or a negative charge (anion), with polyatomic ions frequently being anions.
For example:

• Permanganate ion \( \text{MnO}_4^- \) carries a -1 charge.
• Nitrite ion \( \text{NO}_2^- \) also carries a -1 charge.
• Dihydrogen phosphate ion \( \text{H}_2\text{PO}_4^- \) carries a -1 charge, despite having hydrogen atoms, which are typically positive.
• Ammonium ion \( \text{NH}_4^+ \) is an example of a positively charged polyatomic ion. It carries a +1 charge.
• Phosphate ion \( \text{PO}_4^{3-} \) carries a -3 charge.
• Sulfite ion \( \text{SO}_3^{2-} \) carries a -2 charge.

The charge on an ion dictates how it will pair with other ions to maintain electrical neutrality within a compound.

Nomenclature of Ions

Nomenclature is the systematic way of naming chemical substances. For polyatomic ions, specific suffixes and prefixes are used to indicate variations in the oxygen content of the ions.
Common naming patterns include:

• Ions ending in "-ate" generally have more oxygen atoms than those ending in "-ite". For example, nitrate \( \text{NO}_3^- \) versus nitrite \( \text{NO}_2^- \).
• "Hypo-" and "per-" prefixes indicate fewer and more oxygen atoms respectively. For example, hypochlorite \( \text{ClO}^- \) has fewer oxygen atoms than chlorate \( \text{ClO}_3^- \), while perchlorate \( \text{ClO}_4^- \) has more.
• Adding "bi-" or "hydrogen" indicates the presence of a hydrogen ion, as seen in bicarbonate \( \text{HCO}_3^- \) and dihydrogen phosphate \( \text{H}_2\text{PO}_4^- \).

Understanding this nomenclature allows chemists to deduce the formulas and charges of ions from their names and vice versa.