Polar covalent compounds are compounds in which the electrons are not shared equally between the atoms of the molecule. Differences in electronegativity between elements account for the unequal sharing of electrons in compounds.
Only atoms with the same electronegativity can share electrons equally in a compound. Electronegativity is a measure of how much an atom attracts electrons. In general, electronegativity increases going from left to right and from bottom to top on the periodic table. The most electronegative element on the periodic table is fluorine.
In a covalent bond in which electrons are shared between two or more atoms, the atom with the greater electronegativity, and thus the greater affinity for electrons, exerts more force on the electrons. The electrons spend more time orbiting around the stronger electronegative atom. This unequal sharing of electrons leads to regions of partial negative charges and regions of partial positive charges in a molecule, making this a polar covalent compound.