Mounting the barrier of understanding between the macro event in a chemistry event and the interpretation at the nano level is one the most difficult achievements for both the student and the teacher..
Where does the chemistry teacher start with chemistry? The typical traditional start in UK schools was with the destructive nature of the Bunsen burner with safety to introduce practical work and then onto elements, mixtures and compounds (which is quite a difficult concept) with separation techniques.
Where does the chemistry teacher start with chemistry? The typical traditional start in UK schools was with the destructive nature of the Bunsen burner with safety to introduce practical work and then onto elements, mixtures and compounds (which is quite a difficult concept) with separation techniques.
Chemistry is holistic with each concept affecting another. Quite honestly, you can start anywhere but there is that understanding barrier in the way. Perhaps, like Alex Johnstone in 1966, and Peter Atkins with his 9 “big ideas” you should start as early as possible with the idea that matter is made up of very small particles and what you see at the macro level is a consequence of what is happening at the nano-level. These particles are too small to see directly so you have to use your thoughts, dreams, diagrams etc to concoct visions of what is happening. I see many books/courses which start with "small particles" but the idea is not maintained through the ensuing pages. Both of Johnstone's text books (Chemistry Takes Shape Vol 1-5 in in1966 and Chemistry Takes Shape in 1980) maintained this commitment to the first big idea of Peter Atkins all the way through. Once a teacher starts with this difficult concept, reinforcement of the idea must be maintained. if you wish to read more about big idas see the article by Vincent Talanquer.· .
One year in 1980s, I was given £200 to my department by a satisfied parent. I could have taken the staff out to a local restaurant but instead, I bought a class set of Molymod® models (http://www.molymod.com/). Finding that the students just want to construct a dog or just connect anything to anything (that is fun, but not chemistry), I had to restrict the handing out to a few atoms and bonds at a time in deep sided trays. (But I still got questions like "Does this one exist, Sir? Sometimes there was quite a good aside, eg cyclopropane!!!)
On my visit to the ICCE2018 meeting I came across the superb VISCHEM computer models (http://vischem.com.au/) produced by the Roy Tasker group. Two videos caught my eye immediately because they are a part of my microscale workshops. The precipitation video (http://www.scootle.edu.au/ec/pin/HVFJXB?userid=71715 and scroll to "precipitation of an ionic salt") showed the silver chloride precipitate forming a line (picture below) and I thought that is just like one of my diffusing precipitate videos.
The Vis-Chem video of the macro event at the beginning of the video shows the traditional test tube reaction. The colourless solutions have been already prepared and then mixed with a white precipitate forming.
Now watch the microscale version. Here is the line of silver and chloride ions coming together to form a precipitate. This microscale version though shows the addition of the solids to the puddle and in the space of just over a minute, the whole macro process that the Vis-Chem video describes (and more because this procedure shows the dissolving process) takes place in front of the student in under 2 minutes.
The Vis-Chem video of the macro event at the beginning of the video shows the traditional test tube reaction. The colourless solutions have been already prepared and then mixed with a white precipitate forming.
Now watch the microscale version. Here is the line of silver and chloride ions coming together to form a precipitate. This microscale version though shows the addition of the solids to the puddle and in the space of just over a minute, the whole macro process that the Vis-Chem video describes (and more because this procedure shows the dissolving process) takes place in front of the student in under 2 minutes.
The microscale puddle video shows what happens when silver nitrate and sodium chloride particles are dissolved in water how the ions are solvated by water (see below), breaking up the solid crystal lattice, how the ions move by diffusion using kinetic energy, and ultimately, how the silver chloride forms as a solid.
The second video concerned the displacement reaction between silver nitrate and copper metal (http://www.scootle.edu.au/ec/pin/HVFJXB?userid=71715 and scroll to Redox reactions). The macro experiment in the film shows the action of a colourless solution to copper foil. Silver is formed on the copper and drops off.
Now look at the microscale version under a USB microscope. The silver crystals (like fir trees) can be seen growing outwards.
We are witnessing evidence for the movement of electrons within metals. Why is this important? Because the mechanism happens in other situations
- All displacement reactions, where a more reactive metal displaces a less active metal ion from the solution.
- Some displacement reactions such as magnesium on metal salt solutions, eg iron(II) sulfate, result in the formation of the less active metal but at the same time, bubbles (of hydrogen gas) are seen along with the formation of iron(II) hydroxide precipitate. So there are competing reactions as shown below with electrons reacting with water and with iron(II) ions.
- There is the "puzzling" reaction when zinc and copper metal ae attached together and placed in a dilute acid. The bubbles of hydrogen appear on the copper metal as the electrons move from the zinc to the copper and react with the acid on the surface but it is the zinc metal that dissolves. There must be a lower kinetic barrier for this mechanism as rather than zinc reacting directly with acid. The copper is effectively acting as a catalyst.
The rusting process where there are positive and negative sites on the surface of the metal and rusting accelerated by copper (see photo right) and slowed with zinc and magnesium. You can see more here and scroll down
Aishling Flaherty of Limerick University presented a plenary address on 1st year University students find "curly arrow" explanation of organic chemistry reactions difficult. ‘Twas ever thus. I did it in 1964 and it was tricky to many then. But chemistry then was taught as physical, organic and inorganic with distinct rivalries. Is it still?
Unless the Big Idea of electron movement (with electrons falling into a hole or even a depression “a partial hole”) is used in both inorganic and organic chemistry, we shall still be struggling with the understanding of these concepts. VisChem also looks at some simple organic reactions.
When the questions are asked how and why does this happen, then the Big Ideas of entropy increase and conservation of energy come into being, with the proviso that there may be a kinetic barrier. The molecular shape and intermolecular forces between molecules, especially in water at school level, are crucial in the mechanisms in which electron pairs are attracted to electron deficient (holes) species. There is periodicity because I can carry out these reactions with compounds of elements in the same groups. And it all happens because matter is made up of very tiny particles. It is all very holistic.
Appendix
Looking for connections in inorganic chemistry reactions and indeed, between different branches of chemistry, is a form of “chunking”, a process (see diagram below) in which “individual pieces of information are bound together into a meaningful whole” (Wikipedia). Instead of learning loads of separate facts, you apply basic ideas from which you can ascertain an answer to an exam question. Would it were so simple!
Exams are so important that students are scared of being wrong and teachers are worried for their jobs because they may be blamed for exam failures. It is safer to students to have many “fact cards” to learn by heart.
Application of present knowledge to new situations really throws students, A recent UK examination question about boiled carrots caused consternation because “we had not studied carrots” but they had studied osmosis in potatoes! And osmosis all about matter consisting of very tiny particles, invisible to the naked eye, the first of P W Atkins big ideas.
Aishling Flaherty of Limerick University presented a plenary address on 1st year University students find "curly arrow" explanation of organic chemistry reactions difficult. ‘Twas ever thus. I did it in 1964 and it was tricky to many then. But chemistry then was taught as physical, organic and inorganic with distinct rivalries. Is it still?
Unless the Big Idea of electron movement (with electrons falling into a hole or even a depression “a partial hole”) is used in both inorganic and organic chemistry, we shall still be struggling with the understanding of these concepts. VisChem also looks at some simple organic reactions.
When the questions are asked how and why does this happen, then the Big Ideas of entropy increase and conservation of energy come into being, with the proviso that there may be a kinetic barrier. The molecular shape and intermolecular forces between molecules, especially in water at school level, are crucial in the mechanisms in which electron pairs are attracted to electron deficient (holes) species. There is periodicity because I can carry out these reactions with compounds of elements in the same groups. And it all happens because matter is made up of very tiny particles. It is all very holistic.
Appendix
Looking for connections in inorganic chemistry reactions and indeed, between different branches of chemistry, is a form of “chunking”, a process (see diagram below) in which “individual pieces of information are bound together into a meaningful whole” (Wikipedia). Instead of learning loads of separate facts, you apply basic ideas from which you can ascertain an answer to an exam question. Would it were so simple!
Exams are so important that students are scared of being wrong and teachers are worried for their jobs because they may be blamed for exam failures. It is safer to students to have many “fact cards” to learn by heart.
Application of present knowledge to new situations really throws students, A recent UK examination question about boiled carrots caused consternation because “we had not studied carrots” but they had studied osmosis in potatoes! And osmosis all about matter consisting of very tiny particles, invisible to the naked eye, the first of P W Atkins big ideas.