Valence electrons, located in the outermost shell of an atom, play an important role in driving chemical reactions and forming bonds with other atoms.

Where a shell is not full, the atom can bond with another chemical species. In this way the valency of an atom describes how full the electron shell is and how readily bonds can form.

Furthermore, each atom can both lose and gain electrons, or, in other words, can function as possessing positive and negative valency.

Tokyo Tech researchers show dendrimers that mimic the electron valency of atoms can also mimic polymerisation yielding controlled one and two-dimensional arrays of nanocontainers.