In chemistry, a trigonal pyramid is a molecular geometry with one atom at the apex and three atoms at the corners of a trigonal base, resembling a tetrahedron (not to be confused with the tetrahedral geometry). When all three atoms at the corners are identical, the molecule belongs to point group C. Some molecules and ions with trigonal pyramidal geometry are the pnictogen hydrides (XH), xenon trioxide (XeO), the chlorate ion, , and the sulfite ion, . In organic chemistry, molecules which have a trigonal pyramidal geometry are sometimes described as sp hybridized. The AXE method for VSEPR theory states that the classification is AXE.