, the ball-and-stick model is a molecular model
of a chemical substance
which is to display both the three-dimensional
position of the atom
s and the bonds
between them. The atoms are typically represented by spheres
, connected by rods which represent the bonds. Double and triple bonds are usually represented by two or three curved rods, respectively, or alternately by correctly positioned sticks for the sigma
bonds. In a good model, the angles between the rods should be the same as the angles between the bonds
, and the distances between the centers of the spheres should be proportional to the distances between the corresponding atomic nuclei
. The chemical element
of each atom is often indicated by the sphere's color.
In a ball-and-stick model, the radius of the spheres is usually much smaller than the rod lengths, in order to provide a clearer view of the atoms and bonds throughout the model. As a consequence, the model does not provide a clear insight about the space occupied by the model. In this aspect, ball-and-stick models are distinct from space-filling (calotte) models
, where the sphere radii are proportional to the Van der Waals atomic radii
in the same scale as the atom distances, and therefore show the occupied space but not the bonds.
Ball-and-stick models can be physics|physical
artifacts or virtual computer model
s. The former are usually built from molecular modeling kit
s, consisting of a number of coil spring
s or plastic or wood sticks, and a number of plastic balls with pre-drilled holes. The sphere colors commonly follow the CPK coloring
. Some university courses on chemistry require students to buy such models as learning material.
's 1865 ball-and-stick model of methane
). Later discoveries disproved this geometry.
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
Specialist companies manufacture kits and models to order. One of the earlier companies was Woosters at Bottisham
, 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.
The Beevers Miniature Models
company in Edinburgh
(now operating as Miramodus
) produced small models beginning in 1961
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.
* VSEPR theory