Problem 28 - Chemistry and Chemical Reactivity

Question

The compound \(\mathrm{Na}_{2} \mathrm{O}_{2}\) consists of (a) two \(\mathrm{Na}^{+}\) ions and two \(\mathrm{O}^{2-}\) ions (b) molecules of \(\mathrm{Na}_{2} \mathrm{O}_{2}\) (c) two \(\mathrm{Na}^{+}\) ions and one \(\mathrm{O}_{2}^{2-}\) ion (d) \(\mathrm{Na}^{2+}\) and \(\mathrm{O}^{2-}\) ions

Step-by-Step Solution

Answer

Option (c) is correct: two \( \mathrm{Na}^{+} \) ions and one \( \mathrm{O}_{2}^{2-} \) ion.

Step 1: Analyze the Chemical Formula

The chemical formula given is \( \mathrm{Na}_{2} \mathrm{O}_{2} \). This formula represents a compound made up of sodium (Na) and oxygen (O). The subscript numbers indicate the number of atoms of each element in a molecule of the compound.

Step 2: Identify the Possible Ions

Sodium commonly forms \( \mathrm{Na}^{+} \) ions because it loses one electron to achieve a stable electron configuration. Oxygen typically gains two electrons, forming \( \mathrm{O}^{2-} \), but in peroxides such as \( \mathrm{Na}_{2} \mathrm{O}_{2} \), the peroxide ion \( \mathrm{O}_{2}^{2-} \) is present.

Step 3: Determine the Composition Based on Ions

\( \mathrm{Na}_{2} \mathrm{O}_{2} \) is known as sodium peroxide. It is made up of two \( \mathrm{Na}^{+} \) ions and one \( \mathrm{O}_{2}^{2-} \) ion. This matches option (c): "two \( \mathrm{Na}^{+} \) ions and one \( \mathrm{O}_{2}^{2-} \) ion".

Key Concepts

Understanding Sodium Peroxide (Na₂O₂)

Sodium peroxide, with the chemical formula \( \mathrm{Na}_{2} \mathrm{O}_{2} \), is an ionic compound consisting of sodium and oxygen elements. In this compound, each sodium atom donates an electron, forming two sodium ions \( (\mathrm{Na}^{+}) \), while the oxygen atoms together form a peroxide ion \( (\mathrm{O}_{2}^{2-}) \).

Sodium peroxide serves various purposes, ranging from bleaching agents to disinfectants. Its structure allows it to release oxygen, especially useful in closed environments like submarines, where it can purify the air. This ability to release oxygen also makes it an efficient oxidizing agent in various chemical reactions.

When considering its chemical properties, sodium peroxide is highly reactive and can decompose on contact with water, forming sodium hydroxide and oxygen gas. These characteristics make it valuable yet require careful handling.

The Role of the Peroxide Ion (O₂²⁻)

The peroxide ion \( (\mathrm{O}_{2}^{2-}) \) is a distinctive feature in compounds known as peroxides. Unlike typical oxygen ions \( (\mathrm{O}^{2-}) \), which gain two electrons to stabilize themselves, a peroxide ion is an assembly of two oxygen atoms sharing extra electrons.

In the peroxide ion, each oxygen atom manages to keep some of the extra electron density, resulting in the \(\mathrm{O}_{2}^{2-}\) ion. This added configuration is important because it impacts how peroxides behave chemically. Such ions make peroxide compounds capable of breaking down to release oxygen, a property harnessed in various applications.

• Used in bleaching and cleaning agents.
• Critical in oxygen-delivering drugs and therapy.

Understanding peroxide ions is key to predicting the chemical behavior of peroxides like sodium peroxide.

How Chemical Formulas Represent Compounds

Chemical formulas are the shorthand notations that provide fundamental insights into the composition of compounds like sodium peroxide \( (\mathrm{Na}_{2} \mathrm{O}_{2}) \). They tell us the types and numbers of atoms involved in forming a compound.

In \( \mathrm{Na}_{2} \mathrm{O}_{2} \), the subscript '2' following sodium (Na) indicates two sodium atoms in every molecule. Similarly, '2' following oxygen (O) shows a pair of oxygen atoms. To comprehend ionic compounds further, the elemental symbols and their arrangement inform us about the possible cations and anions, crucial in determining the compound's ionic nature.

• Shows ratio and types of atoms.
• Helps in identifying complex ions like \(\mathrm{O}_{2}^{2-}\).

By breaking down these formulas, one can deduce detailed information about the compound's stability and reactivity.