So - What's the matter with Bohr-Rutherford? May 04 2020, 0 Comments

The Bohr-Rutherford model is a high school staple. But does it help students learn real chemistry? 

The BR model of the atom was designed in 1913 by combining Rutherford's nuclear model with Bohr's wave model. While it was insightful at the beginning of the last century, the BR theory was out-of-date by 1925. Yet it first appeared in high school textbooks between 1955 and 1965. Since then, no one has removed it. Why not?

 We all agree that Teachers like it -  it's easy to design highly focused exercises.   Students like it - it's predictable and easy. Administrators like it - it's easy to generate standardized test questions. But apart from standardized testing, how can a high school student use the BR model?

Real science is concerned with predicting and explaining real world events. Can students use the Bohr model to predict the real properties of sodium? Its soft, shiny, metallic appearance, its chemical activity with water, and its basic behaviour? No! Can students use the Bohr model to explain the chemical properties of chlorine? Its non-metal appearance, its binary molecular structure, its reactivity, and its acidity? No - the Bohr model can't do any of that!

 To a high school student, the Bohr model has virtually no predictive or explanatory properties. Students cannot use it unless an expert, a teacher, shows them how to crudely explain only two things: ionic and covalent bonding. Even then, the student must use the interpretive framework provided by the teacher, a framework that is much more elaborate than the model itself, and a framework that is not available to the students themslves. The students are not, by themselves, able to come up with "full octets" or "stable octets" or atoms "wanting" electrons, or atoms "needing to donate" electrons.

 Pedagogically, the BR model of the atom is a fail. Students cannot build upon the model predict anything more than the teacher demonstrates. Students cannot use the model in any real scientific way!

What can teachers do about it? Teachers must always occupy two roles, and to play both roles simultaneously. Science teachers must be expert at science, and also expert at learning theory. So you, as a teacher, must consider two things.

As scientists, teachers know that the Bohr-Rutherford model is only a representation. A picture. Like any good scientist, when our scientific model fails, we must modify the model on scientific grounds.  

We are both scientists and teachers. When teachers change a model, we must also modify the model on pedagogical grounds We must make the new model suitable for young learners.

If the new model is successful, it must be observably better at making scientific predictions, and more readily learned by the student.

Jim Ross imageI invented the Ross Model of the atom specifically as a pedagogical model of the atom - a scientifically powerful model that is easy for high school students to learn. In the next few entries, I will outline what the Ross model looks like.