J.R. S. answered • 09/30/20
Ph.D. University Professor with 10+ years Tutoring Experience
Let's begin with types of bonds.
Covalent bond is one in which the bonding pair of electrons are shared by each atom. That is to say that 1 electrons comes from one atom and one comes from the other. It could also be that both electrons come from 1 atom, but those electrons are shared by both atoms.
Ionic Bond is one in which the bond is formed by a positive and negative charge attracting each other. This arises when one atom donates and electron to the other leaving a net + and - charge on the respective ions.
Caveat: There really is no completely 100% covalent bon or 100% ionic bond but rather a continuum between the two.
If we now turn our attention to polar vs non polar bonds and compounds.
A polar covalent bond is a bond where there is a large difference in electronegativity between the two atoms. Again, unless the electronegativity values of both atoms are the same, the bond will be, to some degree, polar covalent. But the bond between H and Cl will be more polar than the bond between O and Cl (see EN values for each atom and note the ∆ EN).
A polar covalent compound is a compound (not the bonds between the atoms) that has a separation of charge and depends not only on the atoms, but the geometry of the compound. If you look at carbon tetrachloride, CCl4, the C-Cl bond is a polar covalent bond (∆ EN ~ 0.6). Many text books consider ∆EN > 0.4 to be polar, but this is just a generality. So, each of the 4 C-Cl bonds are considered polar bonds, but the molecule is non polar because of the geometry where each Cl sort of "cancels the effect" of the opposite one. This results in no net dipole moment in the CCl4 molecule. CHCl3 on the other hand would be a polar molecule.
Hopefully this has given you sufficient information where you can now go read about polar molecules and polar bonds to better understand the distinctions.
