Introduction: Models in Chemistry
Analogical models are widely used to describe and explain non-observable objects and processes. Models are thinking tools that encourage us to build meaningful mental representations of abstract ideas.
Models are common in chemistry, however, chemists often treat them as the natural language of chemistry and endow them with some form of reality. Models are not fixed, but are thinking tools.
We use models to predict molecular shapes, explain reactions in terms of collision theory and
visualize the states of matter. It is important to remember that models and analogies are simplified or exaggerated representations that always break down somewhere.
This warning is especially important in chemistry where nearly every description and explanation uses models.
Adapted from: http://www.aare.edu.au/03pap/har03448.pdf
Station 1: Models of Intramolecular vs intermolecular forces AND hydrogen bonding close up
Youtube video: Bonding
http://www.youtube.com/watch?v=GnswLP4t6d0&feature=related
This video uses very simple 2D animations to help explain these intra and inter bonding types. What are the benefits (eg. How do they help us understand?) and limitations (eg. How close are they to the real thing?) of models like these?
Youtube video: Hydrogen bonding
http://www.youtube.com/watch?v=LGwyBeuVjhU&feature=related
The video shows Hydrogen bonding. How does the animation which models the process help your understanding?
How can you explain the trends shown in the graphs?
Why does H2O not fit the trend for the other metal hydrides?
Station 2: Molecular modeling kits – ball and stick models.
Use the reference guide to help you build a number of water molecules correctly.
How would you describe the shape of a water molecule?
Arrange the water molecules to show how they would fit together in a sample of water (think of hydrogen bonding to guide you).
Draw your creation.
How does this help you to understand what water “looks like” at the molecular level?
Fill the plastic tub with a bunch of water molecules. Shake the bucket gently.
What state of water are you modeling here?
Now shake the bucket of water molecules more vigorously, until some of them start to pop out the top of the bucket.
What change of state of water are you modeling now?
What kind of energy are you adding in your model?
Place your water molecules back in the bucket.
Imagine you place an electrical current through the water sample.
What would happen to the water molecules?
Create this using your molecules.
Draw what happened to your water molecules.
What are you modeling?
Now place the modeling kit components back in the box ready for the next group.
Station 3: A trip down memory lane - the development of the atomic model
Summarise in a flow chart, very simply, the key historical philosophers/scientists and their contribution to the atomic model, taken from this website:
http://www.fordhamprep.org/gcurran/sho/sho/lessons/lesson32.htm
How did all of their models contribute to our current understanding of the atom?
Now to focus on Rutherford`s contribution…
Breifly describe his experiment, after reading through this information and the animation:
http://regentsprep.org/Regents/physics/phys05/catomodel/ruther.htm
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Using the information you have from above, state how Rutherfords experiment was a model to help him understand?
If the electrons of an atom actually exist in energy levels (not shells), and if they do not orbit the atom like planets orbit the sun, and if we can`t actually say where they are at any one time (we can only use probabilities, because whenever we try to detect an electron we move it)…
Why do they continue to use the Bohr-Rutherford model in textbooks? And why do we continue to use it in our classwork?
And for just a little extra, why is a Lewis structure useful when we model reactions between elements?
Station 4: Animations and 3D models of compounds
http://www.edinformatics.com/interactive_molecules/carbon_jmol.htm
Scroll down this webpage and make a note of what the following models of compounds are and the benefits and limitations of each:
Wire frame model:
Stick model:
Ball and stick model:
Space filling model:
The models of the various allotropes (forms of) carbon are shown further up the page. What are they? Draw a model of each.
How do the models help you to understand the structure and properties of each of the allotropes?
Go here: http://www.creative-chemistry.org.uk/molecules/structures.htm
Draw the models of iodine and sodium chloride.
What are the benefits and limitations of these models?
Station 5: The particle adventure
Look at this diagram. http://en.wikipedia.org/wiki/File:Particle_overview.svg
What is it showing?
Click through “The Standard Model” – the theory of fundamental particles and forces…
http://www.particleadventure.org/
When you have finished clicking and reading through…
Ponder these two questions and write a response:
1) Is it necessary for us to become particle physicists, and to know the details of the fundamental particles and forces, for us to explain what we observe in the high school science laboratory?
2) It could be said that: The number of protons gives an atom its identity and the number of electrons gives an atom its personality.
From your studies throughout high school science, what could you say to support this statement?