Ball-and-stick 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.

The former are usually built from molecular modeling kits, consisting of a number of coil springs or plastic or wood sticks, and a number of plastic balls with pre-drilled holes.

Some university courses on chemistry require students to buy such models as learning material.

In 1865, German chemist August Wilhelm von Hofmann was the first to make ball-and-stick molecular models.

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.

A plastic ball-and-stick model of proline
The motion of water molecules at room temperature and their transient interactions with each other
Hofmann 's 1865 ball-and-stick model of methane (CH 4 ). Later discoveries disproved this geometry.