Density

http://phet.colorado.edu/en/simulation/density  this is a great little game that allows you to change the mass and volume of different objects and calculate the density.

Remember the formula for Density                        Density = Mass
                                                                                               Volume

Build a molecule

This is a great website which links you to a game where you can build molecules.!!  For Junior Cert Science you need to know how atoms bond using Ionic Bonding and Covalent Bonding.  It shows 3D representations too which makes it easier to visualize.

Have a go!!!

http://phet.colorado.edu/en/simulation/build-a-molecule