- Details
- Written by Deirdre Jennings
- Parent Category: Science
- Category: Science 12-15
- Created: 31 May 2011

**The idea here is that grade 6 and grade 7/8 are both looking at two big questions/mysteries.**

1. Why is the periodic table organised the way it is (it's a rather odd shape)? - BELOW

2. Why do atoms combine in the numbers/combinations they do? - *(see here)*

Both of these are good candidates for application of ENV as the answer to both lies in a number (1 - 8) and number patterns, which are characteristics of each atom.

**These variables are not obvious.**

The material is very abstract there is really nothing in the students' experience to attach it to.

NOTE: Identification of variables in both classes is not a problem, assimilating the vocabulary is, due to it's abstract nature.

The written instruction/strategies will be for question 2 only. i.e. describe a set of instructions to allow anyone to find stable/correct (existing) combinations (molecules) of the first 20 atoms, e.g. H_{2}O (water), HCl, NaCl (table salt) etc.

I'm really not sure which of the tasks will prove to be the more challenging!

** STEP 1.** Formulate a challenge and make sure it can't be completed directly or by simple trial and error approach:

**First** I asked the students if I gave you 100 rectangular shaped cards how would you arrange them? The students came up with 6 arrangements each completely out of their own heads I pointed out **when asked** that they could be symmentrical or not as they chose - Students came up with fab designs very much influenced by whatever they are presently up to in other lessons/outside school e.g. one made patterns in the shape of japanese letters as he is taking lessons at the moment :) - then give each student a copy of a simple **periodic table****.**

**THEN** Pose the **BIG QUESTION**: Why is the periodic table organised the way it is (this allows them to 'see' that the arrangement of the 100+ cards in the periodic table is rather odd...)? asking this question brings us straight to step 2 as there is no way they can answer it right away.

* STEP 2.* The first activity involves students brainstorming (3 mins of think-pair-share) all the situations where the arrangement of something tells us information (

Now in the second activity the students started listing all variables visible on the periodic table - **see here****.** - that means look at each box on the table and see what changes from one box to any other box. *I asked them to list the variables. At this point I also had to share with them the official titles (vocabulary) of some of these variables such as atomic number/mass number etc. but didn't tell them yet what they mean or how to make use of them.*

**They listed all the variables they could find... this was not a problem as they are now used to looking for variables. There were a lot of variables including ones which won't affect the outcome. Keep in mind though no variable is ever discounted just because the teacher knows it will have no bearing on the final outcome, that would defeat the purpose of the exercise!, so font, font size, length of the side of the box,... etc. are all allowed and listed as variables, if the students notice them. The students can cross them off the list later through their own investigations.**

This was my starting point and through a series of activities we built up a more detailed picture of all the information. I asked the BIG questions at the beginning, so they could be fermenting away in their brains while we progressed through some smaller steps. Also this allows the** TA objective of step 3** (evaluating your strategy) as either they have the answer or they don't!

The third activity involves students (in groups of 5 or 6) looking for patterns in the variables they have listed. This is essentially their strategy part, explaining why the PT is arranged the way it is. Unfortunately they don't have enough variables (though they don't know that yet). I didn't spend time on writing out the strategy, but I did insist that they write down any patterns they found in their groups. Then they gave feedback to the class & teacher.

**The students did spot the following; **

the atomic number increases from left to right (L - R) across the table

the atomic number increases as you go from top to bottom (T - B) down the table

the mass number also follows these 2 patterns (with one or two small exceptions out of 100+)

columns alternate odd and even atomic numbers

no pattern in the other variables letters/number of letters/ etc

** STEP 3:** Evaluate your position. They have patterns which explain one part of the arrangement i.e. why the order is H, He, Li, Be and so on. However they realised it doesn't explain why Li is under H why not under He or any other...

H He

Li Be B C N O F Ne

Na Mg Al Si P S Cl Ar

**Why not this arrangement for example?**

H He Li Be

B C N O

F Ne Na Mg

Al Si P S

Cl Ar

as it still fits the patterns they found (increasing atomic number and even/odd atomic number columns).

This leads us back to the drawing board...

** Back to step 2:** considering the variables.

So now they will look more deeply into what the variables (parameters), which they've isolated from the periodic table, are telling us.

Now is the time to teach them what atomic number and mass number tells us and how we can use it to build a model of the atom. Think of it as 'just in time' training because they now need more variables to work with and they are not obvious so the students **want to know** now. The students were allowed to start building the models in class and to finish them for homework (6 each). This allowed me to assess whether or not they had understood the rules of putting the model together (some didn't and needed refresher in the following lesson - much easier though when you're looking at a model they have built).

Once the students have built the models they then sit down again in groups and study/examine/discuss the variables. The number of variables now increases dramatically see here. Note the students have now added position on the periodic table as a variable.

**Now see if you can spot any patterns (or links between variables)... students found lots of new patterns and I mean LOADS, way beyond what I was aiming for in fact, and I had to revise my challenge on the spot namely from spot 2 patterns to find 10 MINIMUM!!! (is this a quicky back to step 1?)...**

I had my objectives in mind, leading from specific patterns, but of course students were looking for any and all patterns without prejudice... and I forgot that...silly me!

**Patterns found were; **(a selection...)

size of the atom increases going down the table

electrons increase by 1 going across a row (and then by 1 going to the next row down) .......and this is the idea of periodicity - central to chemistry

layers increase by 1 going down the table

** Back to step 3:** Although they found many more variables (parameters) none were able to account for the shape of the table. What they did not find yet was the pattern in the outer layer electrons...which will unlock the arrangement mystery...

**REFLECTION: **there are a few points here 1) doing this activity series again I would also have a bank of cards of periodic table elements - to allow students to hold/manipulate them and physically put them into different arrangements - this would i think reinforce the possibility of rearranging them 2) students could easily have gone home and looked up the answer (I told them so point blank because I figured someone would look it up) but I asked them not to and explained why - that if they 'figured it out for themselves' it would last much longer and they would understand it better and... they did not look up the answers (amazing :) I did try to arrange the lessons also to prevent it happening (but as it happened, I didn't need to).

**one further major pattern they found was;**

1st row on table has 2 members - 1st layer of electrons = max. of 2

2nd row on table has 8 members - 2nd layer of electrons = max. of 8

3rd row on table has 8 members - 3rd layer of electrons = max. of 8

**BUT based on their observation of this pattern they decided - without being asked/instructed to continue the same line of reasoning and they made a prediction about the 4th layer of electrons as follows; a number of groups did this independently of each other... **

4th row on table has 18 members - 4th layer of electrons = max. of 18 electrons

which is absolutely correct!

**NOW the students are making PREDICTIONS based on the shape & arrangement of the periodic table?! Excellent! This was also entirely unexpected as an outcome but next time I'll be looking out for it! However I don't think I would ask for predictions as it's more interesting to have them as student initiated activities instead.**

** Back to step 2:** considering the variables.

Now they are struggling looking for an answer to the big question...so I keep telling them the answer will come if you actually make use of the models rather than just looking at them randomly. I was trying to get them to arrange the models in the same way as the periodic table so that the pattern (in outer layers) would become more obvious. I didn't want to tell them so I kept going between the groups repeating that they should USE their models to unlock the table and eventually the groups started arranging the models like the table :) Most of this time the students are talking/discussing/arguing in their groups - they are testing and reformulating ideas the whole time - and if their attention is flagging then try encouragement and if that doesn't work then bribery does (just a gummy bear or two each when they crack the code - for all teams - no 'winner'). I didn't need it but I've used it before when kids are getting frustrated - i think it works just because they don't expect it and it makes them laugh (and of course they like them, especially green ones).

As they start to arrange the models they sometimes need encouragement and provoking questions like - oh nice arrangement now what do this lot have in common - OR - hmmm now why is H above Li and Na why not above F and Cl - what does one option have in common that others don't etc.

They spotted the variable that arranges the table in vertical columns but only by using the models.

* Back to step 3: *The students then wrote down and demonstrated how this works for each column (or as they are known in chemistry each group)

SO now they have solved the riddle of the arrangement using 2 sets of variables (ENV) and they are very happy with themselves... time to consolidate and then bring it back to step 1...make it harder again.

** Consolidation**: First I asked the students to make

** Back to STEP 1:** This is quite easy to make impossible again because of course the man (Mendeleev), who conceived the arrangement, knew NOTHING about electrons/protons etc as they hadn't been discovered yet!!! His arrangement was based on a completely different set of variables and their values?!! It turns out the electrons/protons were the underlying reason but nonetheless he was unaware of their existence. Now the students have to go looking for a completely different set of variables! This time they have to focus on variables & values known in the 19th century :) - chemical and physical properties!!!

** Step 2:** This will take the form of a research exercise to build up a bank of information (chemical and physical properties) which was available about elements at the time when Mendeleev created the periodic table. I'll ask the students to research 2 or 3 elements each to make a card with info about each one. The cards will be the bank for a sorting exercise - to remake the table using that info only. This will happen in Term 1, Autumn 2011...