Carbon tetrachloride, CCl4, and chloroform, CHCl3, are common organic liquids. Carbon tetrachloride’s normal boiling point is 77 °C; chloroform’s normal boiling point is 61 °C. Which statement is the best explanation of these data? (a) Chloroform can hydrogen-bond, but carbon tetrachloride cannot. (b) Carbon tetrachloride has a larger dipole moment than chloroform. (c) Carbon tetrachloride is more polarizable than chloroform.

Verified step by step guidance

1. Identify the key properties of the molecules: Carbon tetrachloride (CCl4) and chloroform (CHCl3). Note that CCl4 is a nonpolar molecule, while CHCl3 is polar due to the presence of a hydrogen atom bonded to a more electronegative chlorine atom.
2. Consider the concept of hydrogen bonding: Chloroform (CHCl3) can form hydrogen bonds because it has a hydrogen atom attached to a chlorine atom, which is electronegative. Carbon tetrachloride (CCl4) cannot form hydrogen bonds as it lacks hydrogen atoms bonded to electronegative atoms.
3. Evaluate the dipole moments: Carbon tetrachloride (CCl4) is a symmetrical molecule with no net dipole moment, while chloroform (CHCl3) has a net dipole moment due to its asymmetrical shape and polar C-H and C-Cl bonds.
4. Analyze polarizability: Polarizability refers to the ease with which the electron cloud of a molecule can be distorted. Larger molecules with more electrons, like CCl4, tend to be more polarizable than smaller ones like CHCl3.
5. Compare the boiling points: The boiling point is influenced by intermolecular forces. Chloroform's ability to hydrogen bond contributes to its boiling point, while CCl4's higher boiling point can be attributed to its greater polarizability, leading to stronger London dispersion forces.

Key Concepts

Boiling Point and Intermolecular Forces

The boiling point of a substance is influenced by the strength of its intermolecular forces. Stronger forces, such as hydrogen bonding or dipole-dipole interactions, typically result in higher boiling points. In this context, understanding how these forces differ between carbon tetrachloride and chloroform is essential for explaining their boiling point differences.

Polarity and Dipole Moment

Polarity refers to the distribution of electrical charge over the atoms in a molecule, which is quantified by the dipole moment. A molecule with a significant dipole moment has a positive and negative end, leading to stronger intermolecular attractions. Recognizing the polarity of chloroform and carbon tetrachloride helps in understanding their boiling points and the nature of their interactions.

Polarizability

Polarizability is the ability of a molecule's electron cloud to be distorted by an external electric field, which affects its intermolecular interactions. Larger and more complex molecules tend to be more polarizable, leading to stronger London dispersion forces. This concept is crucial for comparing the boiling points of carbon tetrachloride and chloroform, as it influences their overall intermolecular forces.