Perhaps the most difficult part of atomic structure to grasp is the current understanding of how electrons are arranged outside the nucleus. Students generally come to chemistry comfortable with the idea of electrons orbiting the nucleus like planets around a sun. Though this idea has been known to be incorrect for nearly 100 years, it persists due to the ease at which people can relate to it. It's helpful to use an analogy to help students understand that electrons move about in three-dimensional space, arranged by increasing potential energy and described by clouds of probability.
In this activity, students will create a visual representation of electron energy levels. The example provided above uses the analogy of a hotel with multiple floors. Students can work with this analogy, or come up with their own. This is a great way to shift students away from the imperfect solar system model into something complicated but more accurate.
Electrons with the least potential energy are found near the nucleus. As the distance between the nucleus and the electrons increases, the potential energy also increases. Where students might be tempted to talk about “rings” of electrons, electrons are actually arranged into energy levels and sublevels. The sublevels are sets of orbitals, clouds of space that predict the 90% chance of locating the electron. These probability clouds are determined mathematically.
Though not a perfect analogy, this can be likened to an electron hotel. The floors of the hotel would represent energy levels, each one farther away from the ground floor, or nucleus. Each floor would have wings that are sublevels and within the wings are rooms, or orbitals. A room may contain 0, 1, or 2 electrons. The hotel would populate the rooms, wings, and floors in order of increasing energy, just as the Aufbau Principle describes the build-up of electrons according to energy.
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Create a visual representation of electron energy levels using a hotel analogy. Each floor is an energy level, with the ground floor being the nucleus.