Question

What are London dispersion forces and how do they arise in a nonpolar molecule? Are London forces typically stronger or weaker than dipole-dipole attractions between polar molecules? Are London forces stronger or weaker than covalent bonds? Explain.

Short answer

London dispersion forces are weak intermolecular attractions arising in all molecules, including nonpolar ones, due to temporary fluctuations in electron density. They are weaker than both dipole-dipole attractions, which are a result of permanent dipoles, and covalent bonds that involve the sharing of electron pairs between atoms.

Step-by-step solution

Defining London Dispersion Forces

London dispersion forces are weak intermolecular attractive forces that arise in all molecules, including nonpolar molecules, due to the temporary random fluctuations in the electron cloud around molecules. They are a type of van der Waals force and are also known as dispersion forces, London forces, or instantaneous dipole-induced dipole forces.

Explaining the Origin of London Dispersion Forces in Nonpolar Molecules

In nonpolar molecules, the electrons are distributed evenly throughout the molecule. However, at any given moment, the electron density might become temporarily uneven, creating an instantaneous dipole. This instantaneous dipole induces a dipole in the neighboring molecule by attracting or repelling its electrons. Now, these two temporary dipoles will experience weak attractive forces, known as London dispersion forces.

Comparing London Forces to Dipole-Dipole Attractions

London forces are typically weaker than dipole-dipole attractions. Dipole-dipole attractions result from the electrostatic interaction between the positive and negative poles of polar molecules, which are permanent dipoles. Due to the more consistent presence of dipoles in polar molecules, dipole-dipole attractions are generally stronger than the temporary dipoles created by London dispersion forces.

Comparing London Forces to Covalent Bonds

London dispersion forces are much weaker than covalent bonds. Covalent bonds involve the sharing of electron pairs between atoms, resulting in a strong and consistent bond. In contrast, London dispersion forces arise from temporary fluctuations in electron density and are generally weaker than either ionic or covalent bonds.

Conclusion

London dispersion forces are weak intermolecular forces that arise in all molecules, including nonpolar ones, due to temporary fluctuations in electron density. These forces are weaker than both dipole-dipole attractions and covalent bonds. While London forces play an essential role in stabilizing nonpolar molecules, they are not as strong as the forces and bonds that result from permanent dipoles or covalent bonding.