This demonstration set of atom models is used in chemistry lessons at secondary schools and gymnasiums for the three-dimensional construction of molecules of inorganic and organic substances. With the models the teacher shows the whole class the spatial arrangement of atoms in a molecule, the shape of the molecule, the type and multiplicity of chemical bonds, and explains the phenomenon of isomerism. The set is intended for frontal demonstration in front of the audience when complex topics of organic and inorganic chemistry are covered: the teacher assembles the models in front of the class and the students observe the demonstration.
The set contains 270 parts: 111 balls that are the models of atoms, 140 rods that represent the bonds, and 18 orbital models, together with a tool for taking the constructions apart. The balls are made of coloured plastic and the rods of plastic and metal. The maximum diameter of an atom is 23 mm, and 12 chemical elements are represented in the set. The colour coding follows generally accepted standards — hydrogen white, carbon black, oxygen red, nitrogen blue and others — so the shape and colour of a ball immediately indicate the chemical element it represents. The holes in each ball are set at angles that reproduce the valence of the corresponding element, which is why an assembled construction conveys the real geometry of the molecule. Single bonds are made with rigid rods, and double and triple bonds with flexible ones: the medium rod for a single bond is 27 mm long, the flexible rod for double and triple bonds is 43 mm long, and the short rod for space-filling models is 11 mm long. Operating conditions are an air temperature of +5 to +40 °C and a relative humidity of 40 to 60 % without condensation. The service life is 5 years and the warranty period is 12 months.
The set includes hydrogen balls, white — 40 pcs, carbon balls, black, with different numbers of holes — 38 pcs, oxygen balls, red — 12 pcs, nitrogen balls, blue — 4 pcs, sulphur balls, yellow — 2 pcs, phosphorus balls, violet — 4 pcs, halogen balls, green — 8 pcs, metal balls, silver — 3 pcs, medium rigid rods for single bonds — 55 pcs, long flexible rods for double and triple bonds — 25 pcs, short rods for space-filling models — 60 pcs, violet orbital models representing p-orbitals — 6 pcs, pink orbital models — 6 pcs, beige orbital models — 6 pcs, a tool for removing the short rods — 1 pc, the passport with the warranty card — 1 pc, and individual transport packaging — 1 pc. The set is supplied as a closed configuration and needs no assembly before first use; nothing beyond the parts listed is included.
To build a molecule the balls of the required elements are selected by colour and by the number of holes, since the number of holes in a ball corresponds to the valence of the element, that is to the number of chemical bonds the atom can form: carbon, the black ball, has four holes and forms four bonds. For a single bond a medium rigid rod 27 mm long is inserted into the hole of the first ball as far as it will go and the second ball is then pushed onto the free end, so that both balls sit tightly on the rod without play. For a double bond two flexible rods 43 mm long are inserted into two neighbouring holes of the first atom and their free ends into two neighbouring holes of the second atom, and for a triple bond three flexible rods are used; the flexible rods form an arc that shows the multiplicity of the bond clearly. Short rods 11 mm long are used for compact space-filling models in which the atoms sit close to one another, which helps students to understand the spatial proximity of atoms in a molecule. After the demonstration the model is taken apart carefully with the supplied tool, which is inserted into the hole beside the rod, and never by pulling the rod out with bare fingers, as this damages the holes in the balls; all parts are then put back into the packaging.
The set contains small parts and is used only for demonstration work under the direct supervision of a teacher or another adult who has been given the appropriate instruction; children under three years of age must not have access to the separate parts, and children must not be allowed to play with the set unsupervised. The atoms and rods have sharp edges at the joining points and are handled with care. The parts are not heated and are not brought near an open flame, are not immersed in organic solvents, sprays, acids or alkaline substances, are not washed in a dishwasher or under running hot water, and are not taken apart with sharp tools or a hammer. Contact with the eyes, mouth and mucous membranes is avoided, and if a plastic part is swallowed or enters the airways a doctor is consulted at once. Parts are wiped with a soft dry cloth to remove dust and chalk residue and, when necessary, washed in warm water with a neutral detergent using a soft brush and dried immediately; abrasive materials, organic solvents, alcohol and chlorine-based agents damage the plastic and the colouring. The integrity of the parts, particularly the holes in the balls and the rods, is checked monthly, damaged parts are withdrawn from use, and the set is stored complete in its original packaging in a dry closed room away from direct sunlight, heat sources and damp.
