You can make the model of water cycle. it is one of the the best models. then there us the atomic structure model of different elements. for that you need a thermocol and some plastic balls.
 To make the atomic stucture of helium take a square piece of thermocol. in the centre place a ball. then draw acircle around the balland it shld be big. on the circle place 2 balls at some distanc. in the centre with a marker pen write the no of protons and nuetrons and in the other 2 balls write electrons. u can also provide other info