http://www.ck12.org Chapter 9. Covalent Bonding
Ion-Ion Interactions
Ion-ion interactions have already been considered in a previous chapter, so we will simply do a short review. These
interactions are most significant in the solid state. When dissolved in water, ions are shielded from one another by
water molecules, making ion-ion interactions less prevalent.
In the solid state, ions interact by forming lattices in which oppositely charged ions arrange themselves in a regular
fashion. In theFigure9.15, the small purple Na ions interlock with the larger green chlorine ions in a pattern defined
by the relative sizes and charges of the two ions. Because each ion has a full positive or negative charge, the forces
holding two ions together are relatively strong.
FIGURE 9.15
Ion-ion interaction to form a lattice.More complex polyatomic ions can also participate in these types of interactions. Sodium acetate (Figure9.16) is
one such material.
FIGURE 9.16
Sodium acetateDipole-Dipole Interactions
Adipoleoccurs when two opposite charges are separated by some amount of distance. We have already seen dipoles
in the form of polar bonds. For example, each O-H bond in water is an example of a dipole; the partial positive charge
on hydrogen is separated from the partial negative charge on oxygen by the length of the bond. Amolecular dipole
is the geometric sum of all the individual bond dipoles in a molecule. In order for a molecule to have a dipole, it
must have at least one polar bond. However, not all molecules with polar bonds have an overall molecular dipole.
Sometimes the dipoles within a molecule will effectively cancel each other out, giving a zero net molecular dipole.
This is often seen in symmetrical molecules.