expanded valence: This subset of the database focuses on nonmetals, but goes beyond the six simplest shapes to include shapes such as square planar, T-shaped, see-saw, trigonal bipyramidal, and octahedral. Central atoms involved in these geometries must use an "expanded valence" involving d-orbitals. This is a great subset to use when studying structure in the context of VSEPR theory. Can you explain the shapes and trends you see?