Extra Electron Repulsion from Lone Pairs

Oct 13, 2025 by wbrum.org 146 views

Introduction

Water, a compound composed of two hydrogen atoms and one oxygen atom, is a fundamental component of our planet's ecosystem. Its unique properties, such as high surface tension and boiling point, make it essential for life as we know it. The molecular structure of water, specifically the angle between the hydrogen atoms, has been a subject of interest in chemistry for decades. In this article, we will delve into the factors that influence the angle between the hydrogen atoms in water and explore why it is slightly less than expected for a tetrahedral shape.

The Tetrahedral Shape: A Brief Overview

A tetrahedral shape is a three-dimensional arrangement of atoms where each atom is bonded to four other atoms, with bond angles of approximately 109.5 degrees. This shape is commonly observed in molecules with a central atom that is bonded to four other atoms, such as methane (CH4) and ammonia (NH3). However, the molecular structure of water deviates from this ideal tetrahedral shape, with the angle between the hydrogen atoms being slightly less than 109.5 degrees.

Extra Electron Repulsion from Lone Pairs

One of the primary factors contributing to the deviation from the tetrahedral shape in water is the extra electron repulsion from the lone pairs on the oxygen atom. In water, the oxygen atom has two lone pairs of electrons, which are not involved in bonding with the hydrogen atoms. These lone pairs occupy space around the oxygen atom, causing repulsion between them and the bonded hydrogen atoms. This repulsion results in a slight decrease in the bond angle between the hydrogen atoms, making it less than 109.5 degrees.

Atomic Radius of the Oxygen Atom

The atomic radius of the oxygen atom is another factor that influences the angle between the hydrogen atoms in water. The oxygen atom has a relatively small atomic radius compared to other atoms in the periodic table. This small radius results in a more compact arrangement of the bonded hydrogen atoms around the oxygen atom, leading to a decrease in the bond angle.

Hybridization of the Oxygen Atom

The hybridization of the oxygen atom is also an important factor in determining the angle between the hydrogen atoms in water. In water, the oxygen atom undergoes sp3 hybridization, which results in a tetrahedral arrangement of the hybrid orbitals. However, the presence of lone pairs on the oxygen atom causes the hybrid orbitals to be slightly distorted, leading to a decrease in the bond angle between the hydrogen atoms.

Comparison with Other Molecules

To better understand the factors influencing the angle between the hydrogen atoms in water, it is helpful to compare it with other molecules that exhibit a tetrahedral shape. For example, in methane (CH4), the carbon atom is bonded to four hydrogen atoms, resulting in a tetrahedral shape with a bond angle of approximately 109.5 degrees. In contrast, the oxygen atom in water has two lone pairs, which cause repulsion and result in a decrease in the bond angle.

Conclusion

In conclusion, the angle between the hydrogen atoms in water is slightly less than expected for a tetrahedral shape due to several factors, including extra electron repulsion from lone pairs, atomic radius of the oxygen atom, and hybridization of the oxygen atom. These factors result in a more compact arrangement of the bonded hydrogen atoms around the oxygen atom, leading to a decrease in the bond angle. Understanding the molecular structure of water is essential for appreciating its unique properties and behavior in various chemical and physical processes.

References

Pauling, L. (1939). The Nature of the Chemical Bond. Cornell University Press.
Cotton, F. A., & Wilkinson, G. (1988). Advanced Inorganic Chemistry. John Wiley & Sons.
Shriver, D. F., & Atkins, P. W. (1999). Inorganic Chemistry. Oxford University Press.

Introduction

In our previous article, we explored the factors that influence the angle between the hydrogen atoms in water, a compound composed of two hydrogen atoms and one oxygen atom. The molecular structure of water is a subject of interest in chemistry, and understanding its unique properties and behavior is essential for appreciating its role in various chemical and physical processes. In this article, we will address some of the frequently asked questions about the angle between the hydrogen atoms in water.

Q: What is the expected angle between the hydrogen atoms in a tetrahedral shape?

A: The expected angle between the hydrogen atoms in a tetrahedral shape is approximately 109.5 degrees. This is because the central atom is bonded to four other atoms, resulting in a symmetrical arrangement of the bonded atoms.

Q: Why is the angle between the hydrogen atoms in water less than expected for a tetrahedral shape?

A: The angle between the hydrogen atoms in water is less than expected for a tetrahedral shape due to several factors, including extra electron repulsion from lone pairs, atomic radius of the oxygen atom, and hybridization of the oxygen atom. These factors result in a more compact arrangement of the bonded hydrogen atoms around the oxygen atom, leading to a decrease in the bond angle.

Q: What is the role of lone pairs in determining the angle between the hydrogen atoms in water?

A: Lone pairs on the oxygen atom play a significant role in determining the angle between the hydrogen atoms in water. The presence of lone pairs causes repulsion between them and the bonded hydrogen atoms, resulting in a decrease in the bond angle.

Q: How does the atomic radius of the oxygen atom influence the angle between the hydrogen atoms in water?

A: The atomic radius of the oxygen atom is relatively small compared to other atoms in the periodic table. This small radius results in a more compact arrangement of the bonded hydrogen atoms around the oxygen atom, leading to a decrease in the bond angle.

Q: What is the significance of hybridization in determining the angle between the hydrogen atoms in water?

A: Hybridization of the oxygen atom is an important factor in determining the angle between the hydrogen atoms in water. The presence of lone pairs on the oxygen atom causes the hybrid orbitals to be slightly distorted, leading to a decrease in the bond angle.

Q: How does the angle between the hydrogen atoms in water compare with other molecules that exhibit a tetrahedral shape?

A: The angle between the hydrogen atoms in water is less than expected for a tetrahedral shape, unlike molecules such as methane (CH4), which exhibit a tetrahedral shape with a bond angle of approximately 109.5 degrees.

Q: What are the implications of the angle between the hydrogen atoms in water for its unique properties and behavior?

A: The angle between the hydrogen atoms in water has significant implications for its unique properties and behavior. The compact arrangement of the bonded hydrogen atoms around the oxygen atom results in a high surface tension and boiling point, making water essential for life as we know it.

Conclusion

In conclusion, the angle between the hydrogen atoms in water is a complex phenomenon influenced by several factors, including extra electron repulsion from lone pairs, atomic radius of the oxygen atom, and hybridization of the oxygen atom. Understanding these factors is essential for appreciating the unique properties and behavior of water in various chemical and physical processes.

References

Pauling, L. (1939). The Nature of the Chemical Bond. Cornell University Press.
Cotton, F. A., & Wilkinson, G. (1988). Advanced Inorganic Chemistry. John Wiley & Sons.
Shriver, D. F., & Atkins, P. W. (1999). Inorganic Chemistry. Oxford University Press.