Please give a definition for each intermolecular force and an example of a molecular compound that would classify for each.

Question

London Dispersion

Dipole-Dipole

Hydrogen Bonding

Ion-dipole

Answer 1

London Dispersion Forces occur between all molecules. These temporary attractions arise due to the random motion of electrons within a molecule so that at any given moment if the electron density at a position in a molecule is great enough, those electrons will repel electrons in neighboring molecules to produce a temporary positive charge so that an electrostatic attraction forms between those molecules.

Dipole-dipole attractions occur between molecules that contain permanent dipoles from the unequal sharing of electrons in the bonds of the molecule. The formation of these dipoles depends on both the geometry and electronegativity of the atoms within the molecule. An example of a molecule which forms Dipole-Dipole bonds with itself is sulfur dioxide. This molecule has bent geometry and two polar covalent bonds between the sulfur and each of the oxygen molecules. Because the dipoles from these bonds do not cancel one another out, these molecules have permanent dipoles: partial positive and partial negative; therefore the sulfur dioxide molecules can form dipole-dipole bonds between the partial negative oxygens and partial positive sulfur.

Hydrogen Bonding occurs between a partial positive hydrogen that gets its charge from a polar covalent bond between the hydrogen and a very electronegative atom: fluorine, oxygen, and nitrogen. The partially charged hydrogen can then form a very strong dipole-dipole bond with a very electronegative atom which has a lone pair of electrons: oxygen, fluorine, or nitrogen. The most common example of hydrogen bonding is water. Water has two polar covalent bonds between the oxygen and hydrogens. These hydrogens have partial positive charges and can form hydrogen bonds with the oxygen of other water molecules.

Ion-dipole interactions will occur between ions (charged molecules or atoms) and molecules with a Dipole moment from polar covalent bonds. A very common example is the interaction between water's oxygen and hydrogen dipoles and the ions of salts such as NaCl. These Ion-Dipole interactions allow the water to pull the ions apart to dissolve the salt.