Water structure and charge distribution — In a water (H2O) molecule, the two lone pairs on oxygen carry which partial charge and why does that matter?

Introduction / Context:
The unique properties of water—high dielectric constant, strong cohesion, and excellent solvent ability—arise from its polar covalent bonds and the electron lone pairs on oxygen. Understanding partial charges explains hydrogen bonding and solvation behavior.

Given Data / Assumptions:

• Oxygen is more electronegative than hydrogen.
• Water has two O–H bonds and two lone pairs on oxygen.
• Geometry is bent (~104.5°), producing a molecular dipole.

Concept / Approach:
Electronegativity difference polarizes O–H bonds: electron density is drawn toward oxygen, giving it a partial negative charge (δ−), while hydrogens carry partial positive (δ+) charges. The lone pairs reside on oxygen, reinforcing its δ− character. These features enable water to act as a hydrogen-bond donor and acceptor and to stabilize ions through ion–dipole interactions.

Step-by-Step Solution:

Verification / Alternative check:
Hydrogen bonding patterns (O as acceptor via lone pairs; H as donor via δ+ on O–H) confirm the charge distribution.

Why Other Options Are Wrong:

• Partial positive: contradicts electronegativity trend.
• “Not important”: false; lone pairs are central to hydrogen bonding.
• “Form covalent bonds in ice”: hydrogen bonds, not new covalent bonds, hold ice crystals together.

Common Pitfalls:
Confusing hydrogen bonds (intermolecular, weaker) with covalent bonds (intramolecular, stronger).

Final Answer:
carry a partial negative charge