Students of organic chemistry have an ongoing need for a comprehensive molecular model kit throughout their high school and university studies. There are many different types and makes of kit available commercially, but generally they are either too restricted in the range of compounds which can be built from them, or else are rather expensive if they have a large number and variety of components.
A very versatile kit can easily be made up using cheap and plentiful household items, at a fraction of the cost of commercial kits. The basic components are plastic Christmas decorations, in the form of strings of small beads, usually metallised in silver, gold, red, green or blue. Two sizes are common, 6 mm and 12 mm diameter. The other items are bamboo satay skewers, 2.5 mm in diameter ( available in most supermarkets ) and plastic tubing with internal diameter 2.5 mm. The tubing may be vinyl, polyurethane or any other moderately flexible plastic. The ink tubes from some types of ball point pens can also be salvaged for this purpose. Other materials needed are a set of acrylic poster paints ( black, white, red, blue, green and yellow are the main colours needed ), plus some clear craft glue suitable for wood and plastics and a spray can of clear acrylic lacquer..
Some tools will also be needed, including a small electric drill, a fine hacksaw, a sharp hobby knife, small paint brushes and a protractor. To make the atom centres, it is necessary to drill holes at the required angles into the plastic Christmas decorations ( referred to hereafter as “balls” ) and glue in short lengths of bamboo skewer, after which the atom centres are painted in the appropriate colours. Drilling the holes accurately will require the use of a simple jig made from a block of wood, so that the stubs can be set up at the common bond angles of 90 0, 109 0, or 120 0. Three types of atom geometry are sufficient for most organic compounds, tetrahedral, octahedral and trigonal bipyramidal. The trigonal bipyramid jig is simpler to make, so let's begin with that.
A hole 10 mm in diameter and 5 mm deep is drilled into a wooden block, and angles of 120 0 are marked off around the circumference of the hole . The edge of the hole is chamfered with a countersink or a sharp knife so that a 12 mm ball will sit snugly in the hole.
A 2.5 mm diameter hole is drilled vertically through the centre of the 10 mm hole.
Using the same drill, a hole is then drilled diametrically through the centre of a ball and a 27 mm length of bamboo skewer glued into this. The ball with its protruding prongs is now located by inserting one of the prongs into the hole in the jig