Bonding, structures and properties
Intermolecular forces of attraction are forces between different molecules.
The intermolecular forces of attraction considered here are:
Van der Waals' forces are forces of attraction which exist between all atoms and molecules. Van der Waals' forces are much weaker than all other types of bonding.
They are only significant in atoms and molecules which have no other types of intermolecular forces of attraction, for example, discrete non-polar molecules and the Group 0 elements.
Van der Waals' forces are a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.
The strength of Van der Waals' forces is related to the size of atoms and molecules.The bigger the atom or molecule the bigger the Van der Waals' force.
Permanent dipole-permanent dipole interactions are additional electrostatic forces of attraction between polar molecules.
Permanent dipole-permanent dipole interactions are stronger than Van der Waals' forces for molecules of equivalent size.
A molecule can be described as polar if it has a permanent dipole. A permanent dipole is due to a difference in electronegativity between the atoms involved in a covalent bond.
The spatial arrangement of polar covalent bonds can result in a molecule being polar.
If the molecule is symmetrical the molecule will be non-polar.
Hydrogen bonds are permanent dipole-permanent dipole interactions.
Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar.
Hydrogen bonds are electrostatic forces of attraction between molecules which contain these highly polar bonds.
A hydrogen bond is stronger than other forms of permanent dipole-permanent dipole interactions but weaker than a covalent bond.
Video clip about how materials change state, from ice melting to sweat evaporating.
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