Question

Which of the following compound is not in gaseous phase at \(25^\circ\text{C}\)?

• A. \(ClF\)
• B. \(BrF_3\)
• C. \(IF_3\)
• D. \(ClF_3\)

Hint:

For interhalogen compounds, increasing molecular size generally increases intermolecular attraction and boiling point. Heavier interhalogens are therefore more likely to exist as liquids or solids at room temperature.

Answer 1

The Correct Option is B

Concept: Interhalogen compounds are compounds formed by the combination of two different halogen atoms. These compounds are generally represented by formulas such as \(XY\), \(XY_3\), \(XY_5\), and \(XY_7\), where \(X\) is the larger and less electronegative halogen atom and \(Y\) is the smaller and more electronegative halogen atom. The physical state of interhalogen compounds depends mainly on:
• Molecular mass
• Strength of intermolecular forces
• Molecular size and polarity
• Boiling point of the compound Compounds having lower molecular mass and weaker intermolecular attractions generally exist as gases at room temperature, whereas compounds with larger molecular size and stronger intermolecular attractions tend to exist as liquids or solids.

Step 1: Analyzing the compound \(ClF\).
\(ClF\) (Chlorine monofluoride) is a small interhalogen molecule formed between chlorine and fluorine atoms.
• It has relatively low molecular mass.
• Weak intermolecular van der Waals forces act between its molecules.
• Therefore, its boiling point is low. As a result, \(ClF\) exists in gaseous state at \(25^\circ\text{C}\).

Step 2: Analyzing the compound \(BrF_3\).
\(BrF_3\) (Bromine trifluoride) contains a heavier central bromine atom and three fluorine atoms.
• Its molecular mass is considerably greater than \(ClF\).
• The molecule is T-shaped and polar in nature.
• Stronger intermolecular attractions are present between molecules.
• Due to these stronger intermolecular forces, the boiling point becomes much higher. Hence, at room temperature (\(25^\circ\text{C}\)), \(BrF_3\) exists as a liquid rather than a gas.

Step 3: Analyzing the compound \(IF_3\).
\(IF_3\) (Iodine trifluoride) is another interhalogen compound.
• Although iodine is heavier, \(IF_3\) is unstable under ordinary conditions.
• In many standard chemistry references and competitive examinations, it is treated among gaseous interhalogen compounds. Therefore, it is not the correct option for the compound that is definitely non-gaseous at room temperature.

Step 4: Analyzing the compound \(ClF_3\).
\(ClF_3\) (Chlorine trifluoride) is a volatile interhalogen compound.
• It has comparatively lower molecular mass than \(BrF_3\).
• It possesses relatively weaker intermolecular attractions.
• Therefore, it remains gaseous at room temperature.

Step 5: Final comparison and conclusion.
Among all the given compounds: \[ ClF,\ IF_3,\ \text{and}\ ClF_3 \] are considered gaseous at room temperature, whereas: \[ BrF_3 \] exists as a liquid because of its stronger intermolecular forces and higher boiling point. Hence, the compound which is not in gaseous phase at \(25^\circ\text{C}\) is: \[ \boxed{BrF_3} \]