Intermolecular Forces (IMF)

Forces of attraction between molecules. Sometimes called an interparticle force. They are caused by attractions from opposing charges in a molecule.

Also referred to as induced dipole-induced dipole forces. All covalent compounds have LDF in effect. If it is a nonpolar covalent compound, it is the only type of IMF in effect. LDFs are the weakest types of IMF. LDFs are caused by temporary dipoles formed by chance in a covalent molecule. This dipoles are formed when the covalently bonded electrons in the molecule are biased towards a certain part of the molecule, generating a temporary partial charge, which in turn can affect other surrounding molecules. These temporary dipole formations occur by chance.

Polarizability is used to determine the strength of LDFs for any given covalently bonded molecule. As the likelihood of dipole formation increases with the amount of electrons, the general trend of polarizability follows the size (and thus amount of electrons) of any given atom. A general rule of thumb would be the atom with the larger atomic number will have the higher polarizability and thus stronger LDFs.

Dipole-Dipole attractions are what allow polar molecules to attract one another. As the partial charges of polar molecules are relatively consistent, they are stronger than LDFs which rely on temporary dipoles. Also, this means that orientation matters for Dipole-Dipole Attractions. The difference of electronegativity determines the dipole's magnitude and thus the strength of the attractions (higher is better.)

Hydrogen bonds are a unique type of Dipole-Dipole Attraction that is categorized by two molecules with a Hydrogen bonded to either a Florine, Oxygen, or Nitrogen atom with one being unpaired. Hydrogen bonds are not Hydrogen atoms covalently bonded with another atom, it is an IMF. They are extremely strong as a result of the high difference of electronegativity between Hydrogen and Oxygen, Nitrogen, and Florine.

Attractions between ions and polar molecules. Strength of attraction depends on Coulomb's law. This force is what allows ionic compounds to dissolve in solution.

Attractions between a polar and nonpolar molecule. The strength increases with the dipole magnitude of the polar molecule and the polarizability of the nonpolar molecule.