Oxygen, in molecules like water (H₂O), has a bent shape primarily due to the repulsion between its electron pairs, both bonding and non-bonding, around the central oxygen atom.
Electron Pair Repulsion and Molecular Geometry
The bent shape of oxygen-containing molecules like water arises from the Valence Shell Electron Pair Repulsion (VSEPR) theory. This theory states that electron pairs, whether they are involved in bonding (bonding pairs) or not (lone pairs), repel each other. To minimize this repulsion, the electron pairs arrange themselves as far apart as possible around the central atom.
Oxygen's Electron Arrangement
Oxygen has six valence electrons. In water (H₂O), oxygen forms two bonds with hydrogen atoms, using two of its valence electrons. This leaves four valence electrons, which form two lone pairs.
The Tetrahedral Arrangement
The four electron pairs around the oxygen atom (two bonding pairs and two lone pairs) arrange themselves in a tetrahedral shape to minimize repulsion. However, the shape of the molecule is determined by the arrangement of the atoms, not the electron pairs.
Lone Pair Repulsion and the Bent Shape
Lone pairs exert a greater repulsive force than bonding pairs. This stronger repulsion pushes the bonding pairs (those connected to the hydrogen atoms) closer together, resulting in a bent shape rather than a linear one. The bond angle in water is approximately 104.5 degrees, deviating from the ideal tetrahedral angle of 109.5 degrees due to the increased repulsion from the lone pairs.
In Summary
The bent shape of oxygen in molecules like water is a direct consequence of the electron pair repulsion around the central oxygen atom, where the two bonding pairs and two lone pairs arrange themselves to minimize overall energy, leading to a bent molecular geometry.
