Periodic Trends

A challenging Chemistry concept is explaining periodic trends, connecting related concepts of radii, ionization energy, electronegativity, electron affinity and melting point. Although data booklets provide empirical values, learners not only fail to appreciate how much work is done by the scientific community over lengthy periods for each point (Khan, 2010), they resort to memorizing trends with little understanding. For example, on practice tests students explain why Fluorine has the highest ionization energy because it is most electronegative (both of which are effects of underlying principles of effective nuclear charge and radii). On explaining radii, they state Fluorine is smallest because atoms get smaller towards the top right corner of the periodic table. Possible misconceptions arise given the order of magnitude in picometers, abstractly described at sizes too small to visualize. Similarities in definitions between ionization energy and electron affinity (and later electronegativity) make learning trends challenging as students attempt to understand key concepts while expected to compare different elements given periodic table arrangement.

A possible T-GEM Cycle might be as follows:

Generate: Define atomic radii and ionization energy so learners have rough idea of what data represent

Evaluate: Present radii data for an individual row (ex. Li to Ne) asking students to find trend between radii and atomic number. A possible conclusions is that atomic radii decreases with more protons, graphing element radii versus atomic number.

Modify: Have students compare whether pattern works for other rows on the periodic table (ex. Na to Ar). Identify discrepancies like: Why is Na bigger than Ne (reviewing number of shells), and Why is Ne bigger than F (introducing electron repulsion).

Evaluate: Present ionization energies for individual periods, asking students to find trend between IE and atomic number. A possible conclusion is that ionization becomes harder with more protons, graphing IE versus atomic number.

Modify: Have students compare whether pattern works for other periods. Identify discrepancies like: Why does Na have lower ionization energy than Ne (reviewing number of shells), and Why is O’s electron harder to remove than N (introducing half filled p stability). Learners can extend trends comparing ionization against radii.

A possible technology contribution would be the ‘Periodic Table’ Chemland simulation: http://employees.oneonta.edu/viningwj/sims/periodic_table.html

Clicking ‘Relative Radius Covalent’, displays relative element radii as bar graphs arranged on the periodic table, using visuals to make sense of raw data. Learners can similarly click ‘Relative Energy First Ionization’ to test whether their discovered patterns are empirically consistent or whether theoretical models need to be reorganized.

*For my final TELE design, I am considering addressing similar concepts but primarily using Excel to graph data to make visual sense of patterns in the data booklet. Compiling information for atomic number, radii, first ionization, electron affinity, electronegativity and melting points, students can identify patterns across individual rows and columns, presenting discrepant events to have students iteratively refine models.

References

Khan, S. (2010). New pedagogies for teaching with computer simulations. Journal of Science Education and Technology, 20(3), 215-232.

4 comments

  1. Hi Andrew,
    This looks like a great lesson. I have to admit it has been a long time since Chem 11 and 12 so the ideas are there but a little hazy from lack of use. I like how you used the T-GEM approach and showed how students return to evaluate and modify again. I wonder how students could show you their learning so that they don’t just end up repeating known facts without the conceptual understanding.
    Your TELE design project sounds interesting, I look forward to seeing the final design.

    1. Thanks Sarah. No worry, apart from what I’m currently teaching my mind is pretty hazy about everything else. Yes I’m playing around with different ways of representing the trends, constructing different graphs with Excel. Haven’t fully worked out what I want to do yet, but hope it comes together soon!

      Andrew

  2. Hi Andrew

    I like the fact that you brought up a topic that nearly all students have a problem with. It is a topic, where the students are given data and are expected to believe what they are told.

    I wonder if there is a way for students to complete a hands-on activity that will help them understand periodic trends.

    A good next step might be, if you have not done so already is to share a student worksheet that goes with http://employees.oneonta.edu/viningwj/sims/periodic_table.html

    Christopher

    1. Thanks for the suggestion Chris. Yes I was impressed by the Chemland suite and will definitely incorporate that into my teaching. I’ve been playing around with manipulating the data using spreadsheets, and perhaps using WISE to walk learners through the trends. Nothing super concrete yet but hope there’s something there.

      Andrew

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