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Covalent bond = a bond in which the electrons are shared by the partner atoms. Polar bond = simply a type of covalent bond in which the electrons are shared but not equally. This happens when two different atoms come together, such a C and O. Each atom has a different ability to draw electrons to itself when it shares electrons (that drawing ability is called Electronegativity). Polar covalent bond = same as a "polar bond". Nonpolar bond = two of the same atoms come together, such as the diatomic molecule N2, or triatomics such as O3, etc. A nonpolar covalent bond could be viewed as having "pure" covalent character. There is perfectly equal sharing. Polar molecule = a molecule in which the polar bonds are disposed in such a way that it imparts an asymmetry to the molecule as a whole. That is, it gives the whole molecule a Dipole Moment: example: water H-O-H has two polar bonds. Since this molecule is Bent, those two polar bonds ADD TOGETHER to produce a molecule with a dipole moment. That is, a polar molecule. example: carbon dioxide O=C=O has two polar bonds also. Since this molecule is Linear, those two polar bonds ADD TOGETHER to cancel each other out, to produce a molecule with NO dipole moment. That is, a nonpolar molecule. example: carbon tetrachloride CCl4 has four very polar bonds but these bonds are pointing to the corners of a tetrahedron, and form a very symmetric arrangement. The polarity cancels itself out, and the molecule is NONPOLAR.