Lewis Structure of Water

Given

• Valence electrons: H = 1, O = 6

• Oxygen is the central atom (least electronegative besides H)

• Octet rule applies to oxygen; hydrogen takes at most 2 electrons

Find

The Lewis structure of H2O and the arrangement of its electron pairs.

Principle

A Lewis structure places every valence electron as bonding pairs or lone pairs so that each atom (except hydrogen) reaches an octet. The central atom is the one that can form the most bonds. Remaining electrons sit as lone pairs on the most electronegative atom, and their placement later determines molecular shape.

Formula

Solution

1. Count valence electrons: 2 H x 1 + 1 O x 6 = 2 + 6 = 8 valence electrons total.

2. Place oxygen in the center and connect each hydrogen with a single bond. Two single bonds use 2 x 2 = 4 electrons.

3. Subtract: 8 - 4 = 4 electrons remain. Place them as 2 lone pairs on oxygen, the most electronegative atom.

4. Verify octets: oxygen has 2 bonding pairs + 2 lone pairs = 8 electrons (octet satisfied). Each hydrogen has 1 bonding pair = 2 electrons (duet satisfied).

5. All 8 valence electrons are used with no leftovers: the structure is H-O-H with two lone pairs on oxygen.

6. Arrangement: 4 electron domains around oxygen (2 bonding + 2 lone pairs), which VSEPR reads as a bent molecular shape.

Unit check

Electron counting is integer bookkeeping: 8 electrons enter the structure, and the finished drawing holds exactly 8 — 4 in bonds, 4 in lone pairs. No fractional or missing electrons are possible.

What this means physically

The two lone pairs on oxygen are the reason water is bent, and that bent shape is the reason water is polar — the dipole moments of the two O-H bonds do not cancel. Tracing back, the entire personality of water (solvent of life, hydrogen bonding, high boiling point) starts with this Lewis structure.