Final answer:
Covalent bonds fall into two categories: nonpolar and polar. Nonpolar covalent bonds have equal sharing of electrons between atoms with similar electronegativities. Polar covalent bonds have unequal sharing due to different electronegativities, creating partial charges that influence the substance's properties.
Step-by-step explanation:
Covalent bonds involve the sharing of electrons between atoms. In a nonpolar covalent bond, this sharing is equal because the atoms involved have similar electronegativities, which is the tendency of an atom to attract electrons. When the electronegativity difference is less than 1.7, the bond is usually nonpolar. For instance, the bond in a molecule of nitrogen gas (N₂) is nonpolar as both nitrogen atoms share the electrons equally.
In contrast, a polar covalent bond occurs when the electrons are shared unequally between the atoms due to a significant difference in electronegativity, resulting in a slightly positive (δ+) and a slightly negative (δ-) charge on either side of the bond. Water (H₂O) molecules are formed with polar covalent bonds, where the oxygen atom has a partial negative charge, and the hydrogen atoms have a partial positive charge. The unequal distribution of charge in polar covalent bonds is a determining factor for many of a substance's characteristics, such as solubility and boiling point.
The bond energy of a covalent bond, which can be used to estimate the enthalpy changes in chemical reactions, refers to the energy that is required to break the bond between two atoms, or the energy released when a bond is formed. Understanding the characteristics of covalent bonds is essential for predicting properties such as bond length, bond polarity, and the behavior of molecules during chemical reactions.