I love teaching with manipulatives.
Whether it be scotch tape, thumbtacks, bubbles, hula hoops, balloons, cardboard, or magnets, physical objects can assist greatly in making that which cannot see, tangible.
In chemistry class specifically, one of the most difficult concepts for students to grasp is the concept of Ionization Energy.
Understood as the minimum amount of energy required to remove an electron, conceptually understanding the pull that an atom's positively charged nucleus has on the surrounding electrons is an important foundation for understanding a myriad of other concepts in chemistry.
Given that a solid understanding of Ionization Energy requires an ability to visually abstract what is happening at the atomic level, it is of no surprise that students struggle with this concept.
Below is a video of great manipulative I have been using to help students better understand Ionization Energy.
By using one magnet as the positively charged "nucleus", another magnet, wrapped in tape and attached to a rubber band as an electron, and cardboard as various energy levels "shielding" the outer electrons from the nucleus, students can easily model the strength of nuclear pull qualitatively (how "hard" it is to remove) and quantitatively (how "far" you can pull the rubber band).
Additionally, by adding cardboard layers (energy levels), the relationship between the distance an electron is from the nucleus and the associated Ionization Energy is easily modeled. Click here (scroll to #14) for an example of how I structured this manipulative in the form of a lesson in my chemistry class this year.