Orbit molecular model kit with booklet, 1981.
© Science Museum / Science & Society Picture Library
Made by Cochranes of Oxford Ltd. This kit enables models of molecular structure to be constructed by connecting 'atoms' to each other by connecting rods 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.