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Scientific Practices Post #1: Model Building

Shelly Belleau's picture
Thu, 08/28/2014 - 18:06 -- Shelly Belleau

At the beginning of the school year, I find that I am especially cognitive about my own teaching and learning philosophy and what it means for a student to engage in my science class. I’m certainly aware of and attend to the content standards and preparing students for college. However, another huge consideration is how my science classroom can be a place where students become empowered citizens and gain agency. In my classes, these two goals are primarily rooted in students doing science as they learn the concepts. I find that when students engage in the process of science by inducing scientific principles from evidence and models, they begin to recognize their own ability to problem solve and establish conclusions.

I believe this learning environment is heavily rooted in scientific practices, especially including: building models, establishing conclusions on the basis of models and evidence, and engaging in argumentation and consensus-building with peers. Through a series of three blog posts, I’d like to share my thoughts about these scientific practices and how we might communicate about these practices to middle and high school students. I’d love to hear your thoughts along the way! Oh, and before we get started, let me emphasize that the best way to communicate these practices with students is by doingthem... but before we can build a classroom environment where students engage in the practices, we need to first establish our own ideas about what the practices entail.

Let’s start with model building…/p>

You may have heard the saying, “A picture is worth a 1,000 words!” Because science is full of things that are difficult to explain, scientists create and apply special types of pictures, or representations, called models to help them understand and explain new phenomena.

A good model can do two important things: (1) it can be used to explain observations from experiments already done; and (2) it can guide the making of predictions about experiments that have not yet been tried. After scientists make their predictions based on a model, they (or other scientists) perform the experiments. If the predictions are consistent with their new observations, scientists keep their model because it describes their new observations. However, if the results of the new experiments differ from the model-based predictions, scientists use the new evidence to modify their model so it can account for the new observations (as well as the previous observations). Their revised model can then be used to make new predictions. Scientists develop confidence in their new model only after it can be used repeatedly to make predictions that are confirmed in new experiments. The process of science is a process of developing, testing and modifying models that can explain observations of the natural world.

Whenever possible, we should not only emphasize learning about a particular model in chemistry, but also emphasize the process of how the model was (or is) used to explain particular observations and how the model could be used to make predictions. Within these realms, we can also have students think about the limitations of the model.

What does this look like in your classroom? How do you have students develop, test, and revise models in your chemistry classes?

Comments

Lowell Thomson's picture
Submitted by Lowell Thomson on

Hi Shelly,

Thanks for the post and introduction to your use of models in your classroom. The new IB curriculum for exams starting in 2016 puts quite a bit of emphasis on the "Nature of Science." It seems only natural that the use of models would fit within that, and in fact based on the syllabus statements it certainly does. I'm hoping to be more deliberate in my use of models this year with my new group of juniors.

One activity we worked on late this week is graphing ionization energies for a number of different groups of atoms, and successive ionization energies for a few elements. This will - hopefully! - lead to the students strengthening their understanding of the electronic structure of atoms, which is in essence a model. I'll be following up on Monday and Tuesday with the classes about this, so this weekend I'm working on how to utilize terminology and ideas that leads them to better understand this model. I'll let you know how it goes.

Lowell

 

 

 

Lowell Thomson

@ThomsonScience

IB Chemistry Teacher

International School Bangkok

Joseph Lomax's picture
Submitted by Joseph Lomax on

Discussion of ionization energy (IE) is a good intro into the idea of models. 

It is all about trends and breaks.  Show the plotting of IE vs. Z typically given in GenChem texts. Show "trend up/break/trend up/break".  Allow that the model may need be refined to account for smaller breaks, but there are clear and large breaks (lower IE) after He, Ne, Ar, Kr, Xe.  Refer to the size and charge of the nucleus and electrons, and guide them through the ideas of charge attraction and see if they can think of something that has an energetic break.  If they do not get it right away, stand on a chair or table and jump off.  Soon enough they will get the idea of allowed levels.  

This is the Big Picture (BP) item they need to carry them through many a model: A trend in energy implies a trend in structure (of some type). In this context, here is an atomic structure that uses what we know about the nucleus (positively charged and small) and electrons (negatively charged and small).  There MUST be some structure that accounts for the energetics.  Move from the big features (shells) to smaller features (subshells and filling of subshells) to the width of these features (the size of subshells and shells).  They are not going to get all the subtleties right away, but they will know they exist and there is a physical reason for them.  

This may not be the time to discuss shielding, but that is a one that aches for student participation in building the model.

Submitted by Spectroscopy So... on

Concerning the use of models in science teaching - it's important that students understand the characteristics of an effective model for understanding a

science concept:

  1. the model used must be well understood by the students.
  2. students need to understand the characteristics of the model that are closely associated with the scientific concept to be learned.
  3. student need to understand the characteristics of the model that are not closely associated with the scientific concept to be learned.

It's helpful to illustrate these points by using a model from he student's own experience. For example, suppose you wanted to explain to someone how the

sport of rugby is played. You could begin asking the students to think about American football (#1) and discuss how rugby is similar to football (#2).

  • the ball used is roughly the same shape as a football.
  • the goal of the the defenders is to tackle the ball-carrier.
  • the goal of the ball carrier is to carry the ball over the end zone to score.
  • etc., etc.

Then there are the differences between football and rugby (#3).

  • rugby players wear no pads.
  • scoring is different
  • size of the playing field is different.
  • everyone on the ball-carrier's team must be behind him. (an extremely important difference)
  • etc., etc.

That last difference allows students to make predictions about how rugby is played - an critical characteristic of an effective scientific model - it means that there is 

no blocking for the ball-carrier and no such thing as a forward pass in rugby.  In other words, rugby is not football.

The example (along with others that can be used - a piano as a model for what a harp is - illustrate all the characteristics of an effective scientific model, making it

easier for students to recognize and understand scientific models.  A terrible model for rugby would be baseball, because there are few if any close connections

between baseball and rugby.