Final answer:
Dipole moments in polar covalent bonds occur due to asymmetric electron distribution between atoms with different electronegativities. The dipole arrow points toward the more electronegative atom, indicating the negative pole.
Step-by-step explanation:
When discussing molecules with polar covalent bonds, we often refer to the concept of a dipole moment, which arises due to an asymmetrical distribution of electron density. This distribution occurs because the atoms involved in the bond have differing electronegativities, resulting in one atom having a partial negative charge (δ-) and the other atom having a partial positive charge (δ+). In other words, the molecule has a dipole when there is an uneven sharing of electrons between the bonded atoms.
dipole arrows are utilized to depict this charge imbalance, with the head of the arrow pointing towards the more electronegative atom, indicating the direction of the negative pole. The tail, marked with a plus sign, denotes the partially positive end that is associated with the less electronegative atom.
The term dipole as used in the question refers to this phenomon of polarized bonds that result in a molecule having separated charges. To complete the given sentence: 'Such bonds are said to have a dipole - this can be illustrated with a special dipole arrow pointing to the more electronegative atom.'