entry level: Using this button, you can explore a subset of the full database that includes just the simplest of molecules and ions. All of the structures are small, and the geometries only go as far as tetrahedral. Only 11 elements--all nonmetals--are included. The entry level is a very good starting point for exploring periodic trends. What does trigonal planar mean? Why are some molecules trigonal planar, while others are trigonal pyramidal? How do bond lengths and angles compare going down a column or across a row?