Water Lewis Structure (H2O)
The water lewis structure shows how valence electrons are arranged in H2O: two O–H single bonds and two lone pairs on oxygen. The goal is to satisfy the duet rule for hydrogen and the octet rule for oxygen while keeping formal charges minimal.
Step 1: Count total valence electrons
| Atom | Number of atoms | Valence electrons per atom | Total contribution |
|---|---|---|---|
| O | 1 | \(6\) | \(1 \cdot 6 = 6\) |
| H | 2 | \(1\) | \(2 \cdot 1 = 2\) |
| Total | \(6 + 2 = 8\) | ||
Total available electrons for the Lewis structure: \(\,8\,\) (that is, \(\,4\,\) electron pairs).
Step 2: Choose the skeleton and place single bonds
- Place oxygen in the center (hydrogen is never a central atom in typical Lewis structures). Use the skeleton \( \text{H–O–H} \).
- Form two single bonds (each bond uses \(2\) electrons): total bonding electrons \(= 2 \cdot 2 = 4\). Remaining electrons \(= 8 - 4 = 4\).
Step 3: Place remaining electrons as lone pairs and check octets
The remaining \(4\) electrons are placed as two lone pairs on oxygen (each lone pair is \(2\) electrons). Oxygen then has:
\[ \text{electrons around O} = \underbrace{4}_{\text{in two O–H bonds}} + \underbrace{4}_{\text{in two lone pairs}} = 8 \] so the octet rule is satisfied. Each hydrogen has \(2\) electrons in its single bond (duet rule).
Visualization: H2O Lewis structure diagram
Step 4: Verify with formal charges
Formal charge for an atom is computed by \[ \text{FC} = (\text{valence e}^-) - (\text{nonbonding e}^-) - \frac{(\text{bonding e}^-)}{2}. \]
| Atom | Valence electrons | Nonbonding electrons | Bonding electrons | Formal charge |
|---|---|---|---|---|
| O | \(6\) | \(4\) | \(4\) | \(6 - 4 - \dfrac{4}{2} = 0\) |
| H (each) | \(1\) | \(0\) | \(2\) | \(1 - 0 - \dfrac{2}{2} = 0\) |
What the Lewis structure implies about shape
The electron-domain picture contains \(4\) regions around oxygen (two bonding pairs and two lone pairs), so the electron-pair geometry is tetrahedral. Because two regions are lone pairs, the molecular geometry is bent (V-shaped), with a bond angle near \(104.5^\circ\).
Final check: total electrons used \(= 8\); octet/duet satisfied; all formal charges \(= 0\). This uniquely supports the standard water Lewis structure.