Discovering the periodic properties of elements – Alla scoperta delle proprietà periodiche degli elementi

Goals: students face with the apparently messy bulge of elements, discovering that there are many properties that vary regularly. They are able to argue main similarities and differences among elements. Basing on their observations they are able to  organize elements in opportune groups that are finally compared  with the groups and the periods of the periodic table

Target: 15-17 year-old students (seconda, terza superiore in Italy)

Time needed: 2 units + homework

Teaching strategy: Inquiry-based approach.

CLIL tasks based on the 4 Cs (Content, Communication, Cognition and Culture) + one (competence)

Content: I’ve proposed this activity when students roughly knew some basic information about periodic table, its history and few details more. They know the structure of an atom, its particles and how electrons are arranged in energy levels or shells. Nothing else was known about why the elements are arranged in such rows and columns (periods and groups). This activity can be therefore considered as introductory for learning what the term periodic property means.

Communication: students work in groups using only English to communicate each other. Reading some basics about the topic and looking for their explanation in the Internet, they learn new terms, subdivided in BICS oriented and CALP oriented.

Cognition. Reasoning, creative thinking and evaluating skills are promoted.

Culture: use of different kinds of original resources, in particular materials from other countries (e.g. textbook from USA chemistry classrooms) make students aware of the role of the scientific culture across the world.

Competence: plot a graph, identify trends, comparing and contrasting, defining, predicting, suggesting ideas, explaining and supposing.

THE CLIL MODULE

FIRST LESSON  UNIT

Engage:

Different steps are proposed, in sequence

1 – Students is given the following chart in photocopy.

The chart include atomic numbers,  symbols, first and second ionization energy (expressed in J)
The chart includes atomic numbers, symbols of the first 36 elements, both first and second ionization energies (expressed in J)

2 – Students are asked to look at the chart trying to identify how it is arranged. They are invited to discuss in groups the best way to represent the data in a graph.

They take notes about the terms they need to communicate ideas in this phase. Terms as “chart” “graph” “plot” “values” “draw” and many others are progressively listed in a basic glossary, including a simple definition or a translation in Italian.

Explore:

1 –  Then students are invited to draw their graph. The time needed to complete this task is actually different because of so diverse math skills among students. The choice of the most suitable unit for representing the 1st and the 2nd IEs (Ionization Energies) for each element struggled students at most. They were suggested to complete their graph at home, in some cases they asked me to use the one produced during the lesson as a draft, whereas the final version was produced for homework.

2 – Some  suggestions helped students to draw the graph correctly, in order to get much more information as possible. In particular:

  • use two different colors
  • use just one graph with a double vertical axis for the two IEs, to make trends more comprehensible
  • Write the symbols of each element next to their precise points not leaving them on the horizontal axis far away from them.
  • If some data were too large to be well represented, they could use the symbology of “out-of-scale”, drawing the line without respecting the real unit given.

HOMEWORK – complete the graph and answer the following tasks: 

1- Give a suitable title to your graph

2- Look at the graph of the first IE: what kinds of patterns do you see?

3- How could you quickly relate the shape of the graph to someone who had not seen it? Try to explain by voice.

4- Complete your glossary with the new terms you need to explain your thinking.

SECOND  LESSON UNIT

Explain:

In the second unit lesson  the students have their complete graph in front of themselves.

1- They have to hidden the graph, then they are asked to sketch the graph with a pen in only five seconds.

Working in group they have to discuss their sketches, trying to check their proposals each other, using terms from their own glossaries that they have to implement with the new ones.

2- Now they have to answer to the following questions about the first IE

  • Where are the ionization energies the largest? the smallest?
  • What happens to the ionization energies as the atomic number increases?

The answers are checked in a whole class discussion.

3- At this moment students are invited to group elements by their ionization energies into four consecutive “periods”, listing the range of atomic numbers in each group.

Now the students are more aware of the real meaning of period.

4- Students are invited to predict what happens in the fifth period on the basis of what they have explained till now.

Elaborate:

The same questions of the Explain steps are now proposed for the second graph, regarding the second IE.

Students are aware of the fact that the second IE is always higher than the first ones. The teacher helps them to understand the why.

Surprisingly, students are astonished discovering that the two graphs have only apparently the same trend. In fact, they discover  that while the first IE of an alkali metal is the smallest, its second IE is the largest instead.

On the contrary, the well known noble gases that have typically the largest first IEs, have quite small second IEs.

As final elaboration students have to resume their observations.

Going further they can predict the behavior of each element regarding the ability to loose electrons or to acquire them, as well as the octet configuration seen as a goal for each atom to reach in order to gain stability from an energy point of view.

Evaluate

This CLIL activity has been evaluated not in a final assessment, but step by step, considering some key points

– use of english in communicating opinions and results

– use of right specific terms to explain concepts

– writing a good glossary, with correct definitions and translation

For content:

– giving correct answers to the questions proposed

– make correct predictions about the role of octet as mean to reach stability

– ability to deduce the presence of other periodic properties for the elements

THAT’S IT!

Hope this CLIL activity enjoys you. In case you would know what are  the expected answers for all the questions, please let me know leaving a comment here.

 Bibliography: Eisenkraft, A. – Active Chemistry. It’s about time. 2007

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