Here's why:

* Polarity: A molecule is polar when one end has a slightly positive charge (δ+) and the other end has a slightly negative charge (δ-). This difference in charge is due to an uneven distribution of electrons.

* Electronegativity: The uneven distribution of electrons arises from the difference in electronegativity between the atoms in the molecule. Electronegativity is the ability of an atom to attract electrons towards itself in a bond.

* Atoms with higher electronegativity attract electrons more strongly, creating a partial negative charge (δ-) around them.

* Atoms with lower electronegativity have a partial positive charge (δ+).

Examples of polar molecules:

* Water (H₂O): Oxygen is more electronegative than hydrogen, resulting in a negative charge on the oxygen atom and a positive charge on the hydrogen atoms.

* Hydrogen chloride (HCl): Chlorine is more electronegative than hydrogen, creating a negative charge on the chlorine atom and a positive charge on the hydrogen atom.

* Carbon dioxide (CO₂): Although each oxygen atom has a negative charge, the molecule is linear and symmetrical. This means the charges cancel out, making the molecule overall nonpolar.

Let me know if you'd like more details about polar molecules or have any other questions!