Sub-Atomic Particle Manipulatives

In order to help students better understand the Bohr Model of an Atom, I used to use M&M's to reflect the basic sub-atomic particles (protons, neutrons, electrons). However, it gets VERY expensive to buy a ton of M&M's every year.

So, I designed manipulatives to signify these different particles and their respective charges ("+" for Protons, "-" for Electrons, and "o" for Neutrons). I have not printed these myself as of yet, but I have incorporated a variety of sizes and printing them all at once or particle by particle.