Final answer:
Groups of valence electrons around a central atom form a molecular geometry that places them as far apart from one another as possible due to electrostatic repulsion, as explained by the VSEPR model.
Step-by-step explanation:
Because their negative charge causes electrons to repel each other, groups of valence electrons around a central atom adopt a molecular geometry placing them as far apart from one another as possible, while still remaining associated with the central atom. This concept is fundamental to the Valence Shell Electron Pair Repulsion (VSEPR) model, which predicts the geometry of most polyatomic molecules and ions. In the VSEPR model, regions of high electron density, such as bonding pairs of electrons, as well as lone pairs, are arranged around the central atom to minimize the electrostatic repulsion between them, leading to the most stable, low-energy molecular structure.
The VSEPR model distinguishes between electron group geometry, which is the arrangement of electron groups (both bonding and nonbonding), and molecular geometry, which describes how the atoms in the molecule are spatially arranged. For example, in a molecule with a central atom surrounded by three electron groups, the groups would repel each other to form a trigonal planar shape. This minimizes repulsions by positioning the electron groups and the atoms they associate with as far apart as possible.