7 Repulsive Steric Forces, Total Intermolecular Pair Potentials, and Liquid Structure

7.1 Sizes of Atoms, Molecules, and Ions

At very small interatomic distances, the electron clouds of atoms overlap, and there arises a strong repulsive force that determines how close two atoms or molecules can ultimately approach each other. These repulsive forces are sometimes referred to as exchange repulsion, hard core repulsion, steric repulsion, or—for ions—the Born repulsion, and they are characterized by having very short ranges and increasing very sharply as two molecules come together. Strictly speaking, they belong to the category of quantum mechanical or chemical forces discussed earlier, and unfortunately there is no general equation for describing ...

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