Definition of Bond Angle
A bond angle in chemistry is the geometric angle formed between two adjacent covalent bonds that originate from the same central atom. It is a critical parameter for describing the three-dimensional shape or geometry of a molecule.
Factors Influencing Bond Angle
Bond angles are primarily influenced by the number of electron domains (bonding pairs and lone pairs) around the central atom, as predicted by VSEPR (Valence Shell Electron Pair Repulsion) theory. Electron domains repel each other, arranging themselves to minimize repulsion, which dictates the angles between the bonds.
Example: Water Molecule (H₂O)
In a water molecule (H₂O), the central atom is oxygen. Oxygen is bonded to two hydrogen atoms and also has two lone pairs of electrons. According to VSEPR theory, these four electron domains arrange themselves in a tetrahedral electron geometry, but the molecular geometry is bent. The H-O-H bond angle is approximately 104.5 degrees, slightly less than the ideal 109.5 degrees for a perfect tetrahedron due to the greater repulsion exerted by the lone pairs.
Importance of Bond Angle
The specific bond angles within a molecule determine its overall molecular shape, which in turn dictates many of its physical and chemical properties, such as polarity, solubility, reactivity, and biological function. Precise bond angles are essential for understanding how molecules interact with each other and how they function in biological systems.