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–inside molecules (bonding) –hold atoms together into molecule intermolecular forces –These are what hold the molecules together in the condensed states –Forces between molecules –They get weaker as phase changes from S –L –G When a substance changes state, molecules stay together but intermolecular forces are weakened
Van der Waals forces are electrostatic forces They operate not only between polar molecules but also between electrically neutral atoms and molecules This is because the movement of electrons in the outer shell of the atoms temporarily leads to charge displacements – and to so-called polarization
Long thin molecules can pack closer to each other than molecules that are more spherical The bigger the 'surface area' of a molecule, the greater the van der Waal's forces will be and the higher the melting and boiling points of the compound will be Van der Waal's forces are of the order of 1 of the strength of a covalent bond
Van der Waals forces (animation) How do Van der Waals forces hold Molecules together? Electrons are constantly moving cloud of electron density Of atoms At any one time the electrons may not be evenly distributed van der forces The temporary dipole in one molecule can The dipole induction occurs between all neighboring molecules van der Waals