Beads as models for smallest particles

In the 1980ies Mahmoud El Marsafy (1927 - 2013) introduced molecule modelling with plastic prayer beads in teacher training at Ain Shams University Cairo:

Videoclip 1 shows molecule modelling using white, black, blue, red and green beads for atoms of H, C, N, O, Cl. In Video clip 2  he demonstrates the tetrahedral structure of the sodium chloride crystal lattice using beads as models of Na and of Cl ions.

Beads of two different colours are welded to layers in which a bead for a sodium ion is surrounded by 4 beads for chloride ions and vice versa.
Three of such layers above each other form a cube with 8 beads for sodium or for chloride at their 8 corners.
Each bead is not only surrounded by 4 beads of the other type but by two more beads in the layer above and below.

First publication: 1999                                                                             Last modification: 09.02.2013