This is a great introductory lesson to have students examine different elements nuclear stability with the "Nuclear App" (free download on the App store). I designed a procedure for students to follow that has them investigate neutron/proton ratios as they see first hand how atoms lose and gain stability through the APP. Adjust the procedure to make sure your students investigate magic numbers or so that it fits the needs of your students. Questions follow to get them thinking and to further identify the band of nuclear stability. This is a great lesson to do before you get into radioactive decay chains (alpha, beta, gamma) and they are doing the discovering! Make sure to have your students download the nuclear app the day before you plan on doing this lesson.