Students will use 6 different colored legos each representing a different element to build various compounds and mixtures. For example, black is hydrogen and grey is oxygen. If you put 2 black lego bricks with 1 grey lego brick, you get a water molecule!
Although I use legos here, other similar building toys can be used, including K’Nex, Duplos, Magna-Tiles, etc. Similarly, the colors I use are not essential, what is essential is that there are 6 distinct colors for the 6 elements.