Final answer:
Atoms held together by covalent bonds are referred to as molecules, which can be formed through polar or nonpolar covalent bonds. Nonpolar covalent bonds share electrons equally, resulting in no charge difference across the molecule.
Step-by-step explanation:
The combination of answers that best completes the following statement: When atoms are held together by covalent bonds, they are typically referred to as molecules. Covalent bonds are the strong electrical attraction that holds together two nonmetal atoms sharing a pair of electrons, one from each atom. This shared pair of electrons is attracted to the positive nuclei of both atoms, creating a stable grouping.
There are two types of covalent bonds: polar covalent bonds and nonpolar covalent bonds. Polar covalent bonds feature an unequal sharing of electrons which causes a slight charge difference across the molecule. In contrast, nonpolar covalent bonds have an equal sharing of electrons between the atoms, so there is no charge separation. Nonpolar covalent bonds form between atoms of the same element or different elements that equally share electrons, resulting in no significant charge difference. For example, the oxygen molecule (O2) is held together by a nonpolar covalent bond.