What does it mean for a substance to be polar?

A substance being polar means that it has a pair of equal and opposite charges, leading to a separation of electrical charge within the molecule. This uneven distribution of electron density causes certain areas of the molecule to have a slight positive charge while others have a slight negative charge. As a result, polar substances interact well with other polar substances, such as water, allowing them to dissolve or mix effectively.

Understanding why a substance is classified as polar is essential, especially in the context of solubility and chemical reactions. For example, water is a polar solvent, which is why it can dissolve many ionic compounds and other polar molecules. This characteristic is crucial in biological systems, and helps in understanding various chemical behaviors in different environments.