what happens when the nucleus of one atom attracts a pair of shared electrons more strongly than the nucleus of the other atom in the bond?

If a molecule is polar as a result of a polar covalent bond, which end is positively charged and which end is negatively charged?

See your post way above this one.

When the nucleus of one atom attracts a pair of shared electrons more strongly than the nucleus of the other atom in a bond, it creates a polar covalent bond. In a polar covalent bond, the electrons are unequally shared between the two atoms, causing one end of the molecule to have a partial positive charge and the other end to have a partial negative charge.

To determine which end of a polar molecule is positively charged and which end is negatively charged, you can apply the concept of electronegativity. Electronegativity is a measure of an atom's ability to attract electrons towards itself in a bond. The more electronegative an atom is, the stronger it attracts the shared electrons.

In a molecule with a polar covalent bond, the atom with a higher electronegativity will have a partial negative charge (δ-) due to pulling the electrons closer to itself. Conversely, the atom with a lower electronegativity will have a partial positive charge (δ+), as it has a weaker attraction for the shared electrons.

For example, in the water molecule (H2O), oxygen (O) is more electronegative than hydrogen (H). As a result, oxygen attracts the shared electrons of each hydrogen-oxygen bond more strongly and gains a partial negative charge (δ-). The two hydrogen atoms, having a weaker attraction for the electrons, acquire partial positive charges (δ+).

So, in a polar molecule, the end with the higher electronegative atom will be negatively charged, while the end with the lower electronegative atom will be positively charged.