Understanding Hybridisation of H₂O: Water

Water (H₂O) is also known as dihydrogen monoxide. Water, as a molecule, is quite simple. It has covalent bonds with two hydrogen atoms. It’s an example of sp³ hybridisation, which is the main reason it has many unique properties.

Let us understand how hybridisation happens in H₂O. Read on to learn how it leads to its bonding and molecular shape.

What is the Hybridisation of H₂O?

Water consists of one oxygen atom and two hydrogen atoms. Apart from this, oxygen also has two lone pairs. Each hydrogen atom is bonded to oxygen, covalently. In order to accommodate the four electron density oxygen has, it undergoes sp³ hybridisation.

Using the Hybridisation Formula

We can determine the hybridisation of water using the simple formula:

formula

Step-by-step calculation:

Valence electrons of central atom (O): 6
Monovalent atoms (H): 2
Negative charge: 0
Positive charge: 0

formula

Interpretation:

Hybridisation number = 4, which corresponds to sp³ hybridisation.

Breakdown of H₂O Hybridisation

Water has a tetrahedral geometry, in accordance with its hybridisation. But in reality, the lone pairs end up taking more space when compared to bonded pairs, which results in a bent shape of the molecule.

Here is a complete understanding of its hybridisation.

Electronic Configuration of Oxygen

The atomic number of oxygen is 8.

The ground state of oxygen :

1s² 2s² 2p⁴

Only two unpaired electrons → sufficient to form two bonds, but lone pair arrangement and geometry are still required

Excited state configuration:

1s² 2s² 2pₓ² 2pᵧ¹ 2p_z¹

Lone pairs remaining → orbitals will now be hybridised for correct geometry

Ground state vs excited state orbital diagram

Formation of Hybrid Orbitals

sp³ hybridisation occurs when 1 s orbital and 3 p orbitals mix.
The result:
→ 4 sp³ hybrid orbitals
→ 2 of the orbitals will be used for σ bonding with hydrogen, left will be occupied with lone pairs

Bond Formation in Water

Each oxygen uses:

2 sp³ orbitals to form σ bond with hydrogen
2 sp³ orbitals hold the lone pairs

Result:

2 σ bonds (O–H)
2 lone pairs
Hybridisation type: sp³
Bond angle: 104.5° (not 109.5° because of lone pair repulsion)
Geometry: V-shape or bent shape

Geometry and bonding of water

Details At A Glance

Property	Details
Molecule	Water (H₂O)
Hybridisation	sp³
Geometry	Bent
Bond angle	104.5°
Bonding	2 σ bonds (O–H), 2 lone pairs
Unhybridised Orbitals	0
Oxygen valency satisfied?	Yes, by forming 2 bonds with each hydrogen atom and having 2 LP

Formal Charge in H₂O

To determine if the Lewis structure of H₂O is stable, we calculate the formal charge on each atom using the formula:

Formal charge = Valence electrons – (Lone pair electrons + ½ × Bonding electrons)

Step-by-step for each atom:

Oxygen (O)

Valence electrons: 6
Lone pairs: 2 (4 electrons, 2 in each pair)
Bonding electrons: 4
(4 electrons from two sigma bonds with H)

Formal charge = 6 – (4 + ½×4) = 6 – (4 + 2) = 0

Hydrogen (H) – each

Valence electrons: 1
Lone pairs: 0
Bonding electrons: 2
(1 single bond with oxygen)

Formal charge = 1 – (0 + ½×2) = 1 – 1 = 0

Thus, all atoms in H₂O carry zero formal charge, confirming that the Lewis structure is stable and correct.

Summing Up

The oxygen in H₂O bonds with hydrogen (2 σ) and also has lone pairs. sp³ hybridisation leads to a tetrahedral shape, but due to lone pair repulsion, the angles get compressed to 104.5°, giving it a bent molecular shape (similar to V-shape).

Frequently Asked Questions

Q1. Why does H₂O have V-shaped geometry?

Oxygen in water has two lone pairs, and since the repulsion between two lone pairs in a system is highest, it affects the O-H bonds and causes them to become compressed, resulting in a bent shape.

Q2. How many σ and π bonds are present in H₂O?

There are 2 σ bonds and 0 π bonds in total.

Q3. What is the shape of water?

Bent, due to lone pair repulsion.

Q4. Is H₂O polar or non-polar?

Water is polar, as the dipoles do not cancel out due to high electronegativity of oxygen.

Q5. What are some uses of water in our lives?

Water is the most essential part of the living and nonliving realm. It has vast usages which include regulating Earth's atmosphere, etc. It is also known as a universal solvent.