Nicholson molecular models with instruction leaflets, 1981.
© Science Museum / Science & Society Picture Library
Made by Labquip of Reading. This type of kit enables models of molecular structure to be constructed by connecting 'atoms' to each other by connecting spokes representing bonds. The number of bonds an atom can form is determined by an element's valency, which is dictated by the number of electrons in the outermost shell of an atom of that element.