New Zealand Science Teacher

Using Science Capabilities in Senior Chemistry

25/08/2017

We have been using science capabilities in junior school science at Hagley Community College since 2015.  We have recently begun to explore how they might look in senior school science classes.  When the level 2 NCEA chemistry classes were about to start learning about Lewis Diagrams, it seemed like a good opportunity to approach the concept with the capability of Interpreting Representations. 

Level 2 Chemistry Activity:

We gave out cards about the first 20 elements of the periodic table.  Each card had a photo of the element, the name, symbol, atomic number, and atomic mass of the element.  Each student also got a mini-whiteboard and pen.  The students had to draw the atomic structure of their element on the whiteboard. Whiteboards were placed on the floor in a periodic table pattern with the photo side of the card on top.  We then had discussions about the following ideas:

• Differences between the physical form shown in the photo of the element and the model of the atomic structure drawn.  Using models in chemistry to represent ideas that are too small for our eyes to see and each model focuses on different things.
• The model of the periodic table we created compared to the complete periodic table on the wall.
• Patterns we noticed in the atomic structures as we moved across and down the periodic table we had created on the floor with teachers particularly highlighting the valence electron patterns.
• I drew the Lewis diagram for Calcium on the board and we discussed the differences between the Lewis model and the atomic structure model with teachers particularly highlighting that we only drew what we wanted to pay attention to.

Mini-whiteboards showing a model of atomic structure commonly used in Level 1 NCEA.  The boards are on the floor in the pattern of the periodic table of the first 20 elements.

Level 3 Chemistry Activity:

An extension of this teaching strategy was used in Level 3 Chemistry. 

• Students were introduced to the basic atom models they were familiar with and we talked about the limitations of each model.
• In the discussion, I introduced the idea of electron spin and sub-orbitals and that this is an extension of Bohr’s model; that allows for the 3D shape of the atom.
• We looked at a few digital representations of the sub orbital shapes and instead of drawing atoms with isometric graph paper we have a system of symbols to represent each orbital shape: s, p, d, and f.

Level 2 Student Outcomes:

Immediately, without looking at rules for drawing Lewis diagrams, every student could draw single atom Lewis diagrams and two atom Lewis diagrams with confidence.  They commented about how “…nice it was not to have to draw all that other stuff.” It was only when molecules of more than 2 atoms had to be drawn did they refer to the rules to find out about central atoms.  Their confidence was so high, even students who had struggled a lot this year found this step within their ability, because they felt it was the first new step of learning during the lesson.

Using science capabilities in this way linked the students understanding to what they already knew, it showed them that the Lewis diagram model was the same as the atomic structure model, with less information included.  This meant that their short-term memory was available to digest the central atom rules and apply them. 

"It's nice not to have to draw all that other stuff."

Level 3 Student Outcomes:

Within one lesson all students understood; not only how to write this configuration but also the configuration of ions. No student complained that we had “lied” and taught them wrong at level one and two, or thought of s, p, d, f as a new concept.  Instead they thought of this Level 3 model as an extension, building on what they already knew.

Teachers noticed:

Students didn’t comment much on learning this way. What was noticeable by teachers was the total lack of comments we normally hear expressing dismay, information overload, or confusion at yet another new thing to learn.  Students have shown that this strategy for learning about Lewis diagrams and s, p, d, and f orbitals, has become deeply embedded in their memory; because they have been able to complete these kinds of chemistry questions several times without having to re-teach these fundamental ideas relating to atomic structure.  Teaching atomic structure using this strategy took less time with both year levels, with students gaining a deep understanding and growing in confidence in less than 2 hours of teaching time.  When atomic structure is taught as an extension of a known representation, students don’t feel that what they have learnt in previous years is “wrong” and so they use that prior knowledge as the anchor for the new knowledge to sit on.