A bond angle is defined as the angle formed between two adjacent atoms in a molecule, specifically involving a central atom and its neighboring atoms. When the central atom has no lone pairs of electrons, it exhibits what is known as an ideal bond angle. This ideal bond angle represents the optimal spatial arrangement that minimizes electron pair repulsion, which is a fundamental principle in molecular geometry.
In cases where the central atom possesses one or more lone pairs, the ideal bond angle is typically reduced. For instance, in a molecule with a central atom bonded to two surrounding atoms, the bond angle is measured between these two bonds. If there are three surrounding atoms, the bond angles are measured between each pair of bonds. The presence of lone pairs alters these angles, as they exert repulsive forces that push the bonded atoms closer together, resulting in a smaller bond angle.
To visualize this, consider a central atom with lone pairs; the bond angles will be represented as smaller angles in diagrams. Understanding how lone pairs affect bond angles is crucial for predicting molecular shapes and behaviors, which are essential concepts in chemistry.