Final answer:
The significance of dipole-dipole forces depends on the size of partial charges within a molecule and the dipole moments. These forces are weaker than ionic bonds and decrease quickly with distance. To evaluate if a molecule is polar or non-polar, check if the net dipole moment is zero or not.
Step-by-step explanation:
Understanding Dipole-Dipole Forces
To determine how significant dipole-dipole forces are, one must consider the partial charges within molecules. The larger the partial charges on the atoms in a bond, the larger the bond dipoles will be, resulting in stronger dipole-dipole forces. Dipole-dipole forces occur between polar molecules, such as a molecule of hydrogen chloride (HCl), which has a partially positive hydrogen atom and a partially negative chlorine atom. These forces are much weaker than ionic bonds because they involve only partial charges. Moreover, the strength of dipole-dipole interactions decreases rapidly as the distance between molecules increases, following a 1/r³ relationship. In contrast, ionic bonds decrease in strength with a 1/r relationship when distance is doubled.
To assess polarity and dipole moments in molecules, find the net dipole moment. If the net dipole moment is zero, the molecule is non-polar; otherwise, it is polar. Stronger dipole-dipole interactions correlate with larger dipole moments, affecting the physical properties of the substance, such as boiling or melting points. For example, HCl exhibits these interactions and is a gas at room temperature, whereas NaCl, with stronger interionic forces, is a solid with a high melting point.