Developing a bar model for ionic formulae

Some time back in March, I stumbled across Ben Rogers’ (@BenRogersEdu) blog post about using the Singapore bar model in Science (Ben’s is here), and the conversations Damien Benney (@Benneypenyrheol) was having on Twitter about his experiences of using bar models in Science. At the time, I was teaching electricity to my Y8 ‘support’ group who were struggling with some of the mathematical concepts in this topic, and I was searching for a way to support them to carry out calculations successfully. I used Ben’s example questions for calculating current in parallel circuits from his booklet, and the ‘I do, we do, you do’ modelling approach advocated in this, and it was a bit of a revelation – my students found the calculations very easy and had no problems following this method.

A little while later, I was observing a PGCE student teaching my Y9s how to write ionic formulae – most of them got it very quickly (they’re a high attaining group) and so didn’t need any support, but one of the quieter students was really struggling with the concepts and wasn’t willing to say so in front of the rest of the class. Without really thinking about it much, it occurred to me that the bar model idea could be used to represent the balancing of charges, so I drew this in her book and talked her through it:

I asked her to then complete an example and explain to me what she was doing, and although she wasn’t very confident in her response, she did get to the correct answer. I got quite excited about this discovery, so I shared it on Twitter, and Damien Benney has now also successfully used it with his students:

As Ben said in his talk at researchED Rugby, the important thing about the bar model is that it is scaffolding the algebra in order to help the students think about the science rather than the maths (I’ve paraphrased here…). I like this example for ionic formula for that reason – it is very easy to get to the correct answer, so students think more about making sure the positive and negative charges balance out in order to get to the correct formula. It also gets away from the method I’ve seen so many people using where you swap the charge from one ion to be the subscript number for the opposite ion in the formula (see below) – this method teaches them a (pretty rubbish) way to get to the answer (most of the time), but doesn’t give them any sense of the science behind it.

More recently, having read through Pritesh Raichura’s (@Mr_Raichura) excellent blog posts on procedural and declarative knowledge (based on his #CogSciSci talk) and on equations in science, I decided to create some handwritten questions and use careful modelling and scaffolding to help my Y10 ‘bottom set’ Chemistry class to learn how to write ionic formulae. We had already done a lot of practice questions on identifying the charges of individual ions and using correct notation in Chemistry in order to prepare them for this next step. I used the visualiser and lined paper to show them how to layout their working, and modelled several questions requiring different numbers of ions to show them how to proceed, getting more and more input from them with each worked example. They then completed this series of questions independently and were (mostly) very successful:

I’m happy to share the question sheets if anyone wants them (haven’t yet worked out how to link the document to this blog post).

The system I used was inspired by Pritesh’s layout for science calculations:

Step 1: identify the formula of each ion in the compound, and write it on the left.
Step 2: Draw a bar for the positive ion – make it wider if it has a bigger charge.
Step 3: Draw a bar for the negative ion underneath this – the width of this bar must be roughly proportional to the positive ion (e.g. a 2- ion would have a bar twice the width of a 1+ ion).
Step 4: Make the two bars equal widths (and therefore equal charge sizes) by adding extra ions as needed.
Step 5: Write next to the bars how many of each ion were needed.
Step 6: Write out the ionic formula using these numbers, including any 1s.
Step 7: Rewrite the ionic formula, removing any 1s.

I found that each of these steps was necessary to make sure my Y10s didn’t miss anything. It was particularly important to write the number of ions next to the bars, because otherwise they wanted to transfer the charge numbers directly to the ionic formula. I think traditionally you’d probably do step 3 and 4 in the opposite order, and I don’t think it would make a difference – I just happened to do it this way in the lesson.

Interestingly, there have been a few comments via Twitter and at researchED Rugby, saying that this method isn’t really a Singapore Bar Model and that it may be problematic in Chemistry teaching, so I just want to comment on these points here too.

Here is an image of what ionic formulae should really look like if we use the bar model in it’s original form:

Effectively, the positive ions and the negative ions add up to make the total charge of zero in the ionic compound. You can immediately divide the bar underneath the compound name into two – half the total will be your positive ions, and half will be your negative ions. The problem with this is that it becomes conceptually more challenging if your students haven’t got a good grasp of positive and negative numbers, and then they can also get very confused about the total bar (‘copper chloride’ in the above example) as it is representing zero, but is wider than 2+. For this reason, I chose to alter the model slightly to make it conceptually more straightforward to understand (after all, this is the whole point of using the bar model in the first point).

The second issue raised was the fact that this could lead to misconceptions surrounding the idea of ionic compounds as individual molecules, rather than the formula representing the ratio of ions within a giant lattice structure. This is where it’s important to give very clear explanations when introducing this approach. My class had already studied giant ionic lattices at this point (in fact, they had theoretically ‘done’ ionic formulae before but without much success) – when introducing this method, I explained that when we work out the ionic formula, what we are actually calculating is the ratio of ions within the giant ionic lattice of this compound, and reminded them that within this lattice there would be massive numbers of each ion in order to form even the smallest crystal.

There was also some concern that this method was too simple, and perhaps some students are capable of working this out without it and these students would be better off being stretched further etc. etc. – of course this is true! This method is designed to scaffold the thinking process for students struggling with the maths. I wouldn’t use it with all my classes, but I would certainly use it with those students who are struggling with the maths.

As an aside: I suspect there could be other issues with using this model for ionic formulae – and I would welcome comments regarding this. I’ll reveal now that I’m not actually a Chemist… I’m a Biologist who has an A level in Chemistry, so my subject knowledge is not as strong as a Chemist’s will be and therefore there might be issues further down the line that I haven’t thought about…

Behaviour System Updates

On Wednesday, I had a double lesson with my most challenging class – I teach quite a few classes that are considered challenging, but this class have been the most consistently difficult class I’ve had since joining the school in January 2017. They are a ‘bottom set’ Y11 group, mostly boys, and I see them once a week for a double split either side of lunch, at the end of a busy and difficult day in my timetable. There are four students in the class who have been permanently removed from all Science lessons due to their persistent disruption and rudeness to the head of department, who now complete their work in an independent study group supervised by SLT.

It’s fair to say that this is the lesson I look forward to least of all each week, and I was fully expecting today’s lesson to be difficult – the four boys from the ‘independent study group’ were going to be in class for the first time in weeks, and I had completely run out of printing credit so couldn’t print off the work I’d planned, leaving me feeling completely underprepared. But then something very strange happened today: they were a pleasure to teach, and they were (almost) all very well behaved.

So what’s different that has allowed them to be a pleasure to teach? A new centralised behaviour system was introduced in November following consultation with staff. At the start of this term it was clear that there were a few loopholes and aspects that needed tweaking (I wrote about this previously here). A few weeks ago the behaviour system was reviewed, and some changes were made which have proven to be quite divisive amongst the staff.

Here is a summary of the behaviour policy, with the new changes in blue:

Consequences & Zero-tolerance:
C1	Name recorded on board – no sanction.
C2	Tick against name – no sanction.
C3	Recorded on board, SLT member called for a conversation with student, 30 minute after school detention set for the same day. Reasons for C1/2/3 recorded on paper by SLT & logged on SIMs in the main office to trigger sending of text message to parents.
C4	Recorded on board, SLT member called to remove student from lesson and take to internal exclusion for the rest of the lesson. Reasons for C1/2/3 recorded on paper by SLT & logged on SIMs in the main office to trigger sending of text message to parents.
Double lessons	No resetting of C1/2/3/4 halfway through a double lesson, even if the double goes either side of break or lunch.
Zero-tolerance offences	If a student commits a ‘zero-tolerance’ offence during a lesson or around the school site at break, lunch or between lessons, then member of SLT called to take them to internal exclusion room for the next 6 lessons (a full day). Student has supervised break and lunch at a different time to the rest of the school. A reintegration meeting with parents is called. Zero-tolerance offences include extreme defiance (including refusing to enter class), leaving class without permission, swearing, physical contact, prejudiced behaviour (e.g. racism), dangerous use of equipment, violent or threatening behaviour (including verbal threats).

 

There are a number of staff in the school who disagree with this behaviour policy, saying that it is awful and victimises students. Most of the people who dislike this new system are members of staff who have worked in the school for a long time, have established good relationships with the students, their families and the community, and therefore don’t necessarily see the same kinds of behaviours that newer members of staff see on a regular basis. Most of the teachers I talk to each day are really positive about the changes, including NQTs and trainees who feel confident about behaviour management as a result.

There are experienced members of staff who are worried that having this school-wide system will deskill less experienced teachers in behaviour management strategies they can use with their classes. The way I see it is that this system gives a supportive framework that allows everybody to manage behaviour successfully in their classroom, much like the scaffolding we use in our teaching to help those just starting out with their writing or with planning scientific investigations – why wouldn’t we want that support to be available? Over time you become less reliant on the scaffolding, but for the sake of other teachers in the school I think it’s really important that we all still use the language and expectations it illustrates. There is still some way to go to make sure everyone is on board – after all for the system to really work, we need every member of staff to be using it consistently.

So, what about my year 11s? I think the most significant aspect of the recent changes is the fact that the consequences don’t reset half way through my double lesson. The whole class made a real effort to get to pd.6 on time at the end of lunch because they knew being late would mean another consequence. This has never happened before! I usually have to mark at least 10 of them in late after lunch. They were sensible and listened well during the practical demonstrations, showing genuine interest in the lesson. They completed all the work asked of them without making a fuss. No one made silly noises, stroked anyone’s leg or disrupted the lesson by repeatedly farting and talking about their latest poo (all pretty standard behaviours for this class). No one was rude, defiant or aggressively argumentative (also pretty standard behaviours for some members of the class). Even with the tighter system, without resetting of consequences over lunch, only one student in the class received a sanction, and that was a zero-tolerance for leaving the class five minutes early before lunch. I cannot stress enough how different they were to teach.

I know this is anecdotal, but I wouldn’t say that the behaviour system is making things awful for these students or victimising them in any way. Instead it has allowed the whole class to have a lesson where they could learn, free from disruption, and with a teacher who was able to teach without the usual stress caused by the poor behaviour of the class. I don’t know about you, but this feels like a win-win situation to me.

A new behaviour system – perspectives from the front line.

To say this year has been a challenge for our school would be a bit of an understatement. We arrived back from the summer holidays to find the headteacher had very suddenly resigned. Results had dropped. We had an interim head (the deputy CEO of the academy trust), who quickly became the permanent head, and it soon became apparent that the school was also in financial trouble and that redundancies were needed.

It’s fair to say that the hope that staff had at the end of the holidays vanished with the sun, and that trust of the school’s leadership was fragile.

Behaviour has been a problem in the last year, and this was something the new head identified very early on. The behaviour system we had in place was complicated and difficult to manage, involving multiple different levels of detentions, department removal room rotas and a focus on restorative justice. He looked at the behaviour systems in some of our partner schools, and established a behaviour focus group to come up with a solution to the problems we had with disruption to lessons. A new system was developed, communicated to parents and students, and a start date set for November. The details of the system are below:

• A centralised detention system, with no personal or department detentions;
• Detentions on the same day as the behaviour, after school;
• Text message alerts for parents to let them know that their child has an after school detention;
• A clear and consistent consequences system – C1 given for first instance of disruption, C2 for a second instance, C3 for third, C4 for fourth;
• C1 and C2 would have no sanction attached and would not be logged (effectively these are warnings);
• C3 would result in a 30 minute detention, be logged on SIMs and a member of SLT would be called to speak to them;
• C4 would result in a 60 minute detention and removal from that lesson by the member of SLT on call.

The kind of behaviours that would be considered disruption were identified – e.g. arriving late to lesson, calling out, not following instructions, not engaging with work, comments to other students etc. Certain behaviours were considered severe enough to skip C1/2 and go straight to C3 (e.g. swearing, defiance etc.).

A very important part of the system is that the member of SLT on call will always back up the teacher who has called them, so it is seen as supportive and there is no reason for a teacher to hesitate when setting a C3 or C4.

I teach Science – often seen as a problem area for behaviour. I have come across many leaders who have blamed behaviour in Science on the quality of teaching, but I think there are very good reasons why behaviour is more of an issue in Science than in many other subjects:

1. Science is a core subject, so we have to teach every student in Y7-11 whether they want to learn Science or not;
2. Science is the least valued of the core subjects in terms of results, input from SLT, intervention, curriculum time, external support, and college course offers (e.g. “I only need a 4 in English and Maths to get on my course, why do I need Science?”);
3. Science departments tend to have a high turn over of staff (for a variety of reasons), which means there are often new members of staff having to establish themselves, unfamiliar with the systems and who don’t yet have good relationships with the students they teach, because these things take time;
4. Science is a practical subject, requiring high standards of behaviour for health and safety reasons. Science teachers are more likely to “sweat the small stuff” in order to maintain high standards.

In my experience so far, this new behaviour system has been very effective, and has made a big impact with the classes I teach. I teach a large proportion of “bottom set” groups (I might write about setting in another blog post…), including 1 in year 8, 1 in year 9, 2 in year 10 and 1 in year 11. One of the year 10 groups I teach was set up for this academic year specifically as a boys behaviour group, to remove the more disruptive students from other classes. I have found that the new behaviour system has made it so much easier to set high expectations with these groups, and to maintain them – the system has clarity and consistency at its heart, and this makes sense to my students. I actually think I set better expectations for behaviour with my lower attaining groups than my higher attaining groups now because the students have had so much practice with this system – they know the drill.

However, in spite of the successes we have experienced with this system, there have been some major problems in establishing this success at a whole school level:

• There doesn’t appear to be a clear consensus on what behaviours constitute disruption – I don’t give much wriggle room in my classroom (because the classes I have need it to be really clear), but this is not consistent within the department, or across the school.
• Lots of teachers have caught themselves saying “if you keep doing that, you’ll have a C1” – but really if you catch yourself thinking that, they should already have a C1.
• There have been several occasions where members of staff have had their decisions undermined by the on call SLT member in front of their classes – unsurprisingly the teachers involved then become less motivated to follow the system correctly (and will lead to more of the occasions in the bullet point above).
• Some students have refused to attend the detentions, but are still in lessons, getting more C3s and C4s that they will happily ignore. The policy states that they will get double the time the next day, and that repeated failure to attend could result in internal or external exclusions – this is quite vague, and has resulted in some students missing multiple detentions without sanction.
• Judgements are being made on HoDs who’s departments have been setting lots of C3 and C4 detentions. It is still being viewed in the sense of “the Science department have set far more C3 detentions than any other department, there is clearly a problem with behaviour in Science, what are you doing about it?”.
• Behaviour at break time, lunchtime and in corridors between lessons is getting worse. The consequences system only applies in lesson time, so staff often feel powerless to deal with poor behaviour out of class.
• Heads of year and heads of department are being pressured into running detentions to deal with behaviour outside lessons, and to deal with homework (currently not covered in the in-class consequences system).

So, here’s what I think we could do to make the behaviour system even better (and any ideas from anyone reading this would be welcome too!):

1. We need to have some whole school training to highlight what we class as disruptive behaviour, so that everyone is on the same page when it comes to giving C1s. It would be really useful to film a lesson where the behaviour system is being modelled in a ‘real’ lesson effectively – the whole staff could then watch it and look for the types of behaviours that are being given consequences. Many teachers are nervous about issuing the sanctions because they haven’t seen the system being used by anyone else.
2. All of SLT need to be on the same page, and agree to support the decisions staff have made in the classroom (this has been better in the last two weeks).
3. The use of C3s and C4s needs to be seen as a positive thing – members of staff who are using the system should be celebrated, and those who are not setting any C3s should be  checked in case they need support to use it (or to confirm that their classes are just working brilliantly!).
4. The policy needs to be really clear on what will happen to students who miss their detention – e.g. “if you miss your detention, you will have a double length detention the following day. If you miss that, you will have one day in isolation, including lunch and break time. If you fail to attend a detention again, you will have one day of external exclusion”. I think it is really important to have a clear escalation for repeated failure to follow the system.
5. Poor behaviour outside of lessons should also lead to a C3.
6. Lack of homework should result in a C1 – often the student will not be able to fully engage in the lesson’s activities if the homework has not completed.