A Level Chemistry OCR Practice Exam

What defines a polar molecule?

1. A molecule with no dipoles present

2. A molecule with symmetrical charge distribution

3. A molecule with an overall dipole

4. A molecule formed by non-polar bonds

The correct answer is: A molecule with an overall dipole

A polar molecule is defined by having an overall dipole moment, which results from an uneven distribution of electron density across the molecule. This can occur when there are differences in electronegativity between the atoms that make up the molecule, causing a partial positive charge on one side and a partial negative charge on the other. Thus, a molecule can be composed of polar bonds, and if these bonds are arranged in such a way that they do not cancel each other out, the molecule will display an overall dipole moment. In essence, this characteristic of having an overall dipole allows polar molecules to interact more effectively with other polar substances, influencing properties such as solubility, boiling point, and melting point. For example, water is a classic polar molecule, as the oxygen atom is more electronegative than the hydrogen atoms, leading to a partial negative charge near the oxygen and partial positive charges near the hydrogens. The other options describe aspects that do not correspond with the definition of a polar molecule. For instance, molecules without dipoles or those with symmetrical charge distribution (regardless of bond type) would not exhibit the properties associated with polar substances, and non-polar bonds alone do not produce the characteristic dipole that defines a polar molecule