What type of intermolecular forces must be overcome in...

What type of intermolecular forces must be overcome in converting each of the following from a liquid to a gas?
(a) $\mathrm{CO}_{2}$
(b) $\mathrm{NH}_{3}$
(c) $\mathrm{CHCl}_{3}$
(d) $\mathrm{CCl}_{4}$

Key Concepts

London Dispersion Forces

These are weak intermolecular forces that arise from temporary fluctuations in the electron density of molecules, which create transient dipoles. They are present in all molecules, but are the only significant force in nonpolar compounds. The strength of dispersion forces increases with greater molecular size and electron count, impacting physical properties such as boiling points and melting points.

Dipole?Dipole Interactions

Dipole-dipole interactions occur between molecules that possess permanent dipole moments due to an uneven distribution of charge. When the positive end of one polar molecule is attracted to the negative end of another, these forces help determine the physical properties of substances, including boiling and melting points. They are stronger than London dispersion forces in molecules of similar size when significant polarity is present.

Hydrogen Bonding

Hydrogen bonding is a special and particularly strong type of dipole-dipole interaction that occurs when a hydrogen atom, covalently bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine, interacts with a lone pair of electrons on a nearby electronegative atom. This bonding significantly increases the boiling and melting points of compounds and plays a critical role in determining the structure and properties of substances such as water and ammonia.

Molecular Polarity and Geometry

Molecular polarity is determined by both the electronegativity differences between bonded atoms and the molecular geometry, which dictates how individual bond dipoles add up. A molecule with a symmetric arrangement may have polar bonds yet result in a nonpolar overall molecule, influencing which types of intermolecular forces are present. Understanding molecular polarity and geometry is essential for predicting whether dipole-dipole interactions or solely London dispersion forces are dominant.

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