They then repeat this for the models down a group. Using the Bohr model cards – Students set out all the Bohr model cards for one period, so they can analyze the trends across a period.But the application of this in calculating effective nuclear charge is tricky, so this model guides them through the reasoning. Model 2 – The Shielding Effect and Effective Nuclear Charge – This basic idea here is intuitive: protons attract the valence (outer) electrons, but inner electrons repel those outer electrons.I made a diagram of a nucleus and an electron to show this, with an equation included to help students make connections with the mathematical relationship. Model 1 – Coulomb’s Law – For any of this to make sense, students need a good foundation of Coulomb’s Law, which basically states that a greater charge and a shorter distance between particles results in a stronger attractive force between those particles.Side note: If you don’t know what POGIL® is, it stands for “process-oriented, guided-inquiry learning.” This method of instruction starts with visual models, then has a list of questions that guides a group of students through the process of understanding the model. I also wanted a focus on how to explain the trends using Coulomb’s Law on AP free response questions. So, POGIL® already has an activity for periodic trends and Coulomb’s Law, but I specifically wanted something to get them using the Bohr model cards. Creating the Model Exploration Activity (fake POGIL®) With the cards made, next I needed some structure for my students to follow in order to make the connections I wanted them to make.