Duluth Labs Expansion Sets allow you to expand the components of any Duluth Labs molecular set to build larger and more complex molecules for General Chemistry, Organic Chemistry, Inorganic Chemistry and Biochemistry. This set will expand your coverage for building amines, amides, amino, aniline and many other functional groups. The Duluth Labs EXP-006 Nitrogen Kit Includes: 16 Nitrogen Atoms – Trigonal Pyramidal (3 bonds) 6 Nitrogen Atoms – Tetrahedral (4 bonds)