how can a partial positive and partial negative charge develop on atoms involved in a covalent bond?

Brief Explanations:

The development is due to electronegativity differences. In a covalent bond, if two atoms have different electronegativities, the more electronegative atom attracts the shared - electrons more strongly. This causes the electron - density to be closer to the more electronegative atom, giving it a partial negative charge ($\delta^-$). The less electronegative atom, with less electron - density around it, develops a partial positive charge ($\delta^+$).

Answer:

The difference in electronegativities of the atoms in a covalent bond causes the more electronegative atom to attract the shared electrons more, resulting in a partial negative charge on it and a partial positive charge on the less electronegative atom.