<P> In 1865, German chemist August Wilhelm von Hofmann was the first to make ball - and - stick molecular models . He used such models in lecture at the Royal Institution of Great Britain . </P> <P> Specialist companies manufacture kits and models to order . One of the earlier companies was Woosters at Bottisham, Cambridgeshire, UK . Besides tetrahedral, trigonal and octahedral holes, there were all - purpose balls with 24 holes . These models allowed rotation about the single rod bonds, which could be both an advantage (showing molecular flexibility) and a disadvantage (models are floppy). The approximate scale was 5 cm per ångström (0.5 m / nm or 500,000,000: 1), but was not consistent over all elements . </P> <P> The Beevers Miniature Models company in Edinburgh (now operating as Miramodus) produced small models beginning in 1961 using PMMA balls and stainless steel rods . In these models, the use of individually drilled balls with precise bond angles and bond lengths enabled large crystal structures to be accurately created in a light and rigid form . </P>

Why is the ball and stick model not a true representation of the structure of potassium sulfide