Final answer:
In covalent compounds, bonding (valence) electrons are shared between atoms to fill their valence shells, often visualized with Lewis diagrams. The sharing can be either equal or unequal, depending on the atoms' electronegativities, leading to nonpolar or polar covalent bonds respectively.
Step-by-step explanation:
In covalent compounds, the bonding (valence) electrons are shared between atoms. This sharing occurs in order to fill the valence shell of each atom, a concept known as the octet rule. The electrons that are shared can be visualized with a Lewis diagram representing the covalent bonds. Each bond involves a pair of electrons, one from each of the two atoms involved in the bond, and these shared pairs are also known as bonding pairs. For instance, in water (H2O), each hydrogen atom shares its one electron with oxygen, which in turn shares two of its six valence electrons, one with each hydrogen.
When atoms with different electronegativities form a covalent bond, the sharing of electrons is not necessarily equal. Atoms with higher electronegativity will attract the shared electrons more strongly, leading to a polar covalent bond. In contrast, atoms of the same element typically share electrons equally, resulting in a nonpolar covalent bond. Atoms may also share multiple pairs of electrons to form double or triple covalent bonds, as seen in oxygen (O2) and nitrogen (N2) molecules, respectively.