Final answer:
The uneven distribution of electrons that leads to molecules having partial charges is known as a polar covalent bond. It occurs due to differences in electronegativity between bonded atoms, leading to partial negative and partial positive charges in regions of the molecule.
Step-by-step explanation:
The term that describes an uneven distribution of electrons in a molecule, leading to distinct portions having partial positive and partial negative charges, is known as a polar covalent bond. Atoms in a polar covalent bond do not share electrons equally because one atom exerts a stronger attraction for the bonding electrons. As a result, the electrons spend more time closer to one atom, making it partially negatively charged (partial negative charge), while the other atom becomes partially positively charged (partial positive charge). A common example of a polar covalent bond is seen in a hydrogen chloride (HCl) molecule, where the chlorine atom carries a partial negative charge due to a higher electron density, and the hydrogen atom has a partial positive charge.
Polar molecules result from these polar bonds when there is an asymmetrical arrangement of these charges within the molecule. Essential concepts such as dipole moment and electronegativity differences explain why some atoms attract electrons more strongly than others, leading to polarization. The entire molecule can be polar or nonpolar, but the presence of polar covalent bonds is indicative of an unequal electron distribution, potentially making the molecule polar if these charges are not symmetrically arranged.