Diatom

Diatoms are enclosed in two shells that fit together like a pillbox.

Diatoms are characterized by a cell wall called a fistula made of silica, which usually has two overlapping sections.

We show here, through a systematic study of the covalent chemical bond covering the entire periodic system, that the maximum bond multiplicity is six. The maximum value is reached by the tungsten diatom, W₂. No other pair of atoms in the periodic system (atomic numbers smaller than about 100) reaches a higher bond order.