Radii Trends

Build atoms of increasing atomic radius by adding protons to the nucleus, and electrons to the atomic orbitals while discovering fill order.


Take a peek inside the Radii Trends game for a brief overview of the concepts covered through gameplay. Learn about the challenge levels, exploratory sandbox, and free teacher resources for use in your chemistry classroom.

Core levels

To successfully build atoms, students must add an equal number of protons and electrons.

When adding electrons to the orbitals, Students explore the patterns of electron fill order (Pauli Exclusion Principle, Hund’s Rule and Aufbau Principle) and electron configuration.

Students are introduced to the periodic trend of atomic radii by being challenged to create atoms of increasing size.


The Radii Trends Sandbox provides an open-ended and exploratory environment for students to freely build and compare atomic radii of atoms. Design your own extension activities using the Sandbox, and encourage your students to earn the built-in Achievements that focus on a specific topic.

Get started

Start integrating Collisions HE into your educational curriculum today.
Scroll to Top
Scroll to Top

Important Notice

It is with regret that we inform you that Playmada has decided to cease operations. After June 30, 2022 we will no longer be able to provide customer support and training for Collisions.

As of July 1st, 2022, Collisions will remain available and free to all educators and students.

Unfortunately, email, phone or training support will not be available. Visit our user support forum at https://playmada.boards.net.

We welcome you to continue making the most of using Collisions for free in your classroom.

Thank you for your support.