A pioneering ball and stick atomic model set, 1860s.
© Science Museum / Science & Society Picture Library
This is a glyptic type model consisting of a wooden box containing variously coloured wooden balls and two types of connectors; U-shaped metal rods, and metal pegs and rubber tubes. Each ball represents an atom of a chemical element, and can be connected to other 'atoms' by means of bonds represented by inserting the connectors in holes in the balls. The number of holes in a ball represents the number of molecular bonds atoms of different elements are able to form. This 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. The set was used to demonstrate the properties of molecules in early scientific lectures.