Intermolecular forces are essential in understanding the interactions between molecules. Ion-dipole forces arise from the electrostatic attraction between a charged ion and a neutral molecule with a dipole, with strength increasing as the ion'
The set of attractive and repulsive forces that occur between molecules
They strength of the intermolecular forces determines the following physical properties of molecular compounds:
Solubility in various solvents
Hardness and Texture
Surface Tension
Boiling Point
Melting Point
Physical state of a compound at a specific temperature and pressure
London Dispersion
In this example, the uneven distribution of electrons in the He atom (left) causes a temporary dipole (middle). This induces a dipole in the neighboring He atom (right).
The force of attraction acting between all entities, including polar molecules, non-polar molecules and unbonded atoms, caused by the temporary imbalance of electrons within the entities
Larger the molecule, the greater the polarizability
The greater the polarizability, the stronger the dispersion forces
Weakest intermolecular force
Temporary dipole induces a dipole into neighboring molecules
Hydrogen Bonding
In this example, the partially negative oxygen atom in one of the water molecules is attracted to the partially positive hydrogen atom in another nearby water molecule
The force of attraction between a hydrogen atom attached to a highly electronegative atom (N, O, or F) and a highly electronegative atom in another molecule
Important in the organization of biological molecules
Stronger than dipole-dipole or dispersion forces
Positive charge is attracted to the negative charge of an electronegative atom in a nearby molecule
Dipole-dipole interaction
Induced Dipole-Dipole
In this example, the water molecule (polar) induces a dipole into the oxygen molecule (non-polar) which results in a weak attraction between the two.
The force of attraction that forms when a polar molecule induces a dipole in a non-polar molecule by disturbing the arrangement of electrons
A weak form of attraction
Dipole-Dipole
If the dipoles of a molecule cancel each other out, then the molecule is non-polar and symmetrical. If not, then the molecule is polar and asymmetrical
In this example, the partial negative charge of the chlorine atom attracts to the partial positive charge of the hydrogen atom of the other compound.
The force of attraction between the slightly positive end of one polar molecule and the slightly negative end of an adjacent polar molecule
Only has a significant effect when the molecules involved are close together
Increase with an increase in the polarity of the molecule
Weaker than ion-dipole forces
Occurs between neutral polar molecules
Ion-Dipole
Example:
In this example, the oxygen atom in the water molecule has a slightly negative charge and is attracted to the positive sodium ion.
The electrostatic interaction between a charged ion and a neutral molecule that has a dipole
Attraction becomes stronger as either the charge on the ion increases, or as the magnitude of the dipole of the polar molecule increases
