| 摘要 |
A teaching aid comprising a plurality of discs, each with a front (2) and a rear (3) face, and one or more edges (4, 5, 6, 7). The front face (2) having a chemical symbol printed thereon and one or more lines (10) indicating the valency of the chemical entity printed thereon. The size of the disc (1) and the positions of the lines (10) on a disc is such that if necessary a disc may accommodate adjacent abutting discs (1). Certain discs (1) also indicate the charge of the chemical species thereon by the positions of the lines on the left or right hand side of the disc (1) for negative and positive charges respectively.
|
