Final answer:
The partial charge on oxygen in a water molecule is negative due to oxygen's higher electronegativity, which attracts electrons more strongly than hydrogen, leading to a partial negative charge on oxygen and partial positive charges on hydrogen.
Step-by-step explanation:
The partial charge on oxygen in a water molecule is negative. This occurs because oxygen is more electronegative than hydrogen, meaning it has a greater tendency to attract electrons towards itself. When oxygen and hydrogen form a water molecule (H₂O), the electrons shared in the covalent bonds are pulled closer to the oxygen atom. As a result, the oxygen atom obtains a partial negative charge, while the hydrogen atoms obtain partial positive charges. This partial negative charge on the oxygen is indicated by the Greek letter delta (δ) followed by a minus sign, and the partial positive charges on the hydrogen atoms have a delta followed by a plus sign.