Exploring Lone Pair Angles in H2O: Understanding VSEPR Theory

[alingy1]

Homework Statement

What are the angles between lone pairs in H2O? I know that the bonds are separated by 109.5°. What about the lone pair angles? I googled everything. I found nothing. I cannot directly assume it is 109.5°... I have a basic knowledge of VSEPR.

 

[DrDu]

I know that the bonds are separated by 109.5°.

Really? I thought it was 104.45 degrees.
In VSEPR, both bonding and lone pairs should be distributed approximately along the corners of a tetrahedron. Lone pairs are a bit more space filling than bonding pairs, so that the angle between the lone pairs is somewhat larger.

 

[Treedude]

I will double check my answers before posting.

 

[Borek]

H2O is bent. 109.5

H₂O is bent, but 109.5 is incorrect. Water molecule is not tetrahedral. DrDu already posted a correct value.

 

[DeeNos]

Thank you for your question. The angles between lone pairs in H2O can vary depending on the specific geometry of the molecule. In VSEPR theory, lone pairs are treated as electron domains and their repulsion with other electron domains, such as bonding pairs, determines the overall shape of the molecule.

In the case of H2O, the molecule has a bent shape with a bond angle of approximately 109.5°. This angle is determined by the repulsion between the two bonding pairs of electrons. However, the lone pairs also contribute to the overall shape of the molecule.

The lone pairs in H2O are located on the oxygen atom, which has a total of four electron domains (two bonding pairs and two lone pairs). The lone pairs repel each other and also repel the bonding pairs, resulting in a slight decrease in the bond angle. This leads to an estimated lone pair angle of around 104°, slightly smaller than the bond angle of 109.5°.

It is important to note that these angles are not exact and can vary slightly due to factors such as bond length and electronegativity. However, understanding VSEPR theory can provide a good estimate of the angles between lone pairs in H2O and other molecules.

I hope this helps to clarify the concept of lone pair angles in H2O and the role of VSEPR theory in understanding molecular geometry. Please let me know if you have any further questions or need clarification on any of the concepts discussed.