Understanding bond polarity is very important for predicting how molecules act. Here are a few key points to help you understand:

1. Electronegativity Differences:

   • Polar bonds happen when the difference in electronegativity between atoms is greater than 0.4. For example:
     • The C–H bond has a difference of 0.4, so it's nonpolar.
     • The H–Cl bond has a difference of 0.9, so it's polar.

2. Molecular Shapes:

   • The shape of a molecule (like straight, bent, or pyramid-like) affects its dipole moments.
   • Some shapes, like symmetrical molecules (for example, CO₂), can balance out dipole moments, making them nonpolar.

3. Interactions:

   • Polar molecules have dipole-dipole interactions. This affects their boiling and melting points. For instance:
     • Water (which is polar) boils at 100°C, while methane (which is nonpolar) boils at -161.5°C.

These points show why bond polarity is key to understanding how molecules interact and behave.