Question

When acetonitrile, \(\mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{N}:\), a molecular compound, is evaporated what type of particle is in the gas phase? How does this compare to the salt sodium chloride?

Short answer

In the gas phase, acetonitrile exists as neutral molecules, while sodium chloride, which is ionic, would theoretically exist as separated ions if it were possible to vaporize it without decomposition.

Step-by-step solution

Analysis of Acetonitrile Evaporation

Acetonitrile, \( \mathrm{CH}_{3}-\mathrm{C} \equiv \mathrm{N}: \), is a molecular compound with covalent bonds between its atoms. When it evaporates, it forms individual acetonitrile molecules in the gas phase without dissociating into ions.

Comparison to Sodium Chloride

Sodium chloride is an ionic compound composed of \( \mathrm{Na}^{+} \) and \( \mathrm{Cl}^{-} \) ions. When sodium chloride is melted or dissolved in water, its ionic lattice breaks down and it dissociates into individual sodium and chloride ions.

Contrasting Gas Phase Particles

In the gas phase, acetonitrile exists as neutral molecules, whereas sodium chloride, if it could be vaporized without decomposition, would exist as separate \( \mathrm{Na}^{+} \) and \( \mathrm{Cl}^{-} \) ions. In practice, when heated to high temperatures where vaporization would occur, sodium chloride tends to decompose rather than forming a gas of discrete ionic particles.

Key concepts

Acetonitrile Gas Phase Particles

Understanding the behavior of acetonitrile upon evaporation can provide insights into the nature of molecular compounds. Acetonitrile (\( \text{CH}_3\text{C}\text{\textequiv N}: \) is a compound with covalent bonds, meaning the atoms share electrons to form stable molecules. When it evaporates, the process can be envisaged like a gentle lifting where the intact molecules transition from a liquid to a gas phase. The vapor is composed purely of acetonitrile molecules retaining their covalent structure.

Each molecule remains neutral, without breaking down into charged particles. Especially when comparing with ionic compounds, this preservation of molecular identity is key. This concept is part of the broader understanding of how molecular compounds behave when they change states, especially during vaporization.

Ionic vs Covalent Compounds

Distinguishing between ionic and covalent compounds is fundamental in chemistry, as their behaviors are significantly different in various conditions. Ionic compounds, such as sodium chloride (\( \text{Na}^+\text{Cl}^- \) are made of oppositely charged ions held together by electrostatic attractions in a lattice structure. These bonds grant them high melting and boiling points, and in solid form, they often form crystals.

In contrast, covalent compounds, like acetonitrile, consist of atoms linked by shared electrons. They typically have lower melting and boiling points and can exist in a variety of forms, including liquids and gases. When dissolved or melted, ionic compounds split into their constituent ions, whereas covalent compounds maintain their molecular structure. Understanding these differences is crucial when predicting the properties and reactions of substances in different states.

Vaporization of Sodium Chloride

The vaporization of sodium chloride (\( \text{NaCl} \) presents a different scenario than that of molecular compounds. Sodium chloride's strong ionic bonds create a solid lattice framework, requiring significant energy to overcome. Upon heating, instead of forming a gas of \( \text{Na}^+ \) and \( \text{Cl}^- \) ions, sodium chloride tends to break down because the energy required to vaporize is often enough for decomposition.

The theoretical gas-phase particles of sodium chloride, if it could vaporize before decomposing, would consist of separate sodium and chloride ions. However, this is a rarity, as extreme conditions are necessary to reach sodium chloride's boiling point without decomposition. These nuances highlight the distinct ways in which ionic compounds behave under high temperatures compared to molecular compounds.