The Valence Shell Electron Pair Repulsion VSEPR theory is a model used to predict the molecular geometry and bond angles of molecules based on the repulsion between electron pairs in the valence shell of the central atom. Lone pairs of electrons have a significant effect on the bond angles in a molecule.Lone pairs are electron pairs that are not involved in bonding, and they occupy more space around the central atom than bonding pairs. This is because lone pairs are only attracted to one nucleus the central atom , while bonding pairs are attracted to two nuclei the central atom and the bonded atom . As a result, lone pairs repel other electron pairs more strongly than bonding pairs do.According to VSEPR theory, electron pairs in the valence shell of the central atom will arrange themselves to minimize repulsion, which in turn determines the molecular geometry and bond angles. When there are lone pairs present, they will cause the bond angles between the bonding pairs to be smaller than expected.To predict the effect of lone pairs on bond angles using VSEPR theory, follow these steps:1. Determine the total number of valence electrons for the molecule.2. Identify the central atom and distribute the remaining electrons as bonding pairs and lone pairs.3. Determine the electron pair geometry by considering both bonding pairs and lone pairs around the central atom.4. Predict the molecular geometry by considering only the positions of the bonding pairs.5. Determine the bond angles based on the molecular geometry. If there are lone pairs present, the bond angles will be smaller than the ideal angles for the given geometry.For example, in ammonia NH3 , nitrogen is the central atom with one lone pair and three bonding pairs. The electron pair geometry is tetrahedral, but the molecular geometry is trigonal pyramidal due to the presence of the lone pair. The ideal bond angle for a tetrahedral geometry is 109.5, but the presence of the lone pair causes the H-N-H bond angle to be slightly smaller, approximately 107.