Here's why:
* Unequal sharing: In a polar molecule, one atom attracts the shared electrons more strongly than the other atom. This is because the atom with the stronger attraction has a higher electronegativity.
* Partial charges: The atom with the stronger pull acquires a slightly negative charge (δ-) and the other atom acquires a slightly positive charge (δ+).
* Dipole moment: This separation of charge creates a dipole moment, where the molecule has a positive and a negative end.
Example: Water (H₂O) is a polar molecule. Oxygen has a higher electronegativity than hydrogen, so it pulls the shared electrons closer to itself. This creates a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
Other examples of polar molecules include:
* Ammonia (NH₃)
* Hydrogen chloride (HCl)
* Carbon dioxide (CO₂) (despite its linear structure)
It's important to remember that even though the sharing isn't perfectly equal in polar molecules, the electrons are still *shared*, meaning it's a covalent bond. The unequal sharing simply leads to a separation of charge within the molecule.
