Final answer:
Polar covalent bonds result from unequal sharing of electrons due to differing electronegativities between atoms, while hydrogen bonds, although weaker, are crucial for the structure of biological molecules.
Step-by-step explanation:
When one atom participating in a bond has a stronger affinity for the electron, this produces a partial negative charge on one atom and a partial positive charge on the other. These polar covalent bonds should not be confused with the weaker hydrogen bonds that are critical for the three-dimensional structure of biological molecules and for interactions between these molecules.
Polar covalent bonds involve an unequal sharing of electrons because atoms have different electronegativities. An atom with higher electronegativity attracts the shared electron pair closer, resulting in electron density being higher around this atom and thus it acquires a partial negative charge. Conversely, the atom with lower electronegativity will have less electron density around it and thereby gains a partial positive charge.
For instance, in a hydrogen chloride (HCl) molecule, the chlorine atom has a higher electronegativity than the hydrogen atom. Therefore, electrons in the H-Cl bond spend more time near the chlorine atom, giving it a partial negative charge and hydrogen a partial positive charge. In contrast, hydrogen bonds are intermolecular forces that occur between polar groups and are generally weaker than covalent bonds but are extremely important for the structural integrity of complex molecules like DNA and proteins.