Final answer:
Valence shell electron pair repulsion (VSEPR) theory is used to predict molecular shapes by assuming electron pairs repel each other to minimize energy, determining the molecule's three-dimensional structure.
Step-by-step explanation:
The concept used to predict the shapes of molecules, stating that electron pairs repel each other, is known as valence shell electron pair repulsion (VSEPR) theory. The VSEPR model assumes that electron pairs surrounding an atom, both bonding and nonbonding, will arrange themselves to minimize repulsion, thereby determining the molecular geometry. This leads to a predictable arrangement of atoms in space, thus giving the molecule its three-dimensional shape.
It is vital to distinguish between the electron group geometry, which is concerned with the spatial arrangement of all electron groups, and the molecular geometry, which describes how atoms are arranged relative to each other in a molecule. While both aspects are interrelated, molecular geometry can be directly inferred from the electron group arrangement.
Summarizing, the VSEPR model is a valuable tool for predicting the shapes of molecules that helps understand the molecule's physical and chemical properties.