There are many different non-metallic elements that can join together in a polar covalent bond, forming such compounds as water, carbon dioxide and hydrochloric acid. Other types of compounds that contain polar covalent bonds include amines and peptides.
In water, one oxygen molecule forms double polar covalent bonds with two molecules of hydrogen. Hydrochloric acid, or HCl, is formed by a polar covalent bond between one atom of hydrogen and one atom of chlorine, while carbon dioxide consists of one atom of carbon joined to two atoms of oxygen.
Polar covalent bonds are formed when two non-metallic atoms with different electronegativity join together. In this type of bond, the atoms join together by sharing an electron pair. However, due to the difference in electronegativity, the electron is not shared equally. This results in the shared electron pair being closer to the nucleus of whichever atom has the higher electronegativity. The unequal sharing results in one atom gaining a slight positive charge and the other having an equal negative charge.
This type of bond can only occur when the difference in electronegativity is between 0.4 and 2.0. If the difference is less than 0.5, the atoms normally form a non-polar covalent bond, while ionic bonds are formed when the difference is greater than 2.0.