(b) An AB4 molecule has two lone pairs of electrons on the A atom (in addition to the four B atoms). What is the electron-domain geometry around the A atom?

Key Concepts

Electron-Domain Geometry

Electron-domain geometry refers to the spatial arrangement of all electron domains (bonding and lone pairs) around a central atom in a molecule. It helps predict the shape of the molecule based on the number of electron pairs, whether they are involved in bonding or are lone pairs. The geometry is determined using the VSEPR (Valence Shell Electron Pair Repulsion) theory, which states that electron pairs will arrange themselves to minimize repulsion.

VSEPR Theory

VSEPR theory is a model used to predict the geometry of individual molecules based on the number of electron pairs surrounding their central atoms. According to this theory, electron pairs, including lone pairs and bonding pairs, repel each other and will arrange themselves in a way that maximizes the distance between them. This results in specific molecular shapes, such as tetrahedral, trigonal bipyramidal, or octahedral, depending on the number of electron domains.

Lone Pairs and Their Influence

Lone pairs are pairs of valence electrons that are not involved in bonding and are localized on a single atom. They occupy space and exert repulsive forces on other electron domains, influencing the overall geometry of the molecule. In the case of the AB4 molecule with two lone pairs on the A atom, these lone pairs will affect the arrangement of the bonding pairs, leading to a specific electron-domain geometry that differs from that of a molecule with only bonding pairs.