Valence Electrons Are Free To Move
Separate aluminum atoms keep their valence electrons to themselves.
But when a large collection of Al atoms are gathered together, the valences overlap and blend. The loosely held valence electrons are easy to move from atom to atom. This is what makes the metals metallic.
Metals Conduct Electricity
When a voltage is applied to a metal, the loosely held electrons are free to move away from the negative terminal and toward the positive. Small core charge and large valence radius make metals conduct electric current.
Metals Conduct Heat
When a metal is heated, the electrons receive the largest portion of kinetic energy. Because they are free to move, the fast electrons carry the kinetic energy throughout the metal very efficiently.
Metals Reflect Light
Light is an electromagnetic wave. Because the electrons are loose and free to move, the electromagnetic wave causes them to move back and forth at the same frequency. The moving electrons generate a new electromagnetic wave that obeys the laws of reflection!
Metals are Malleable
In a metal, the atomic cores are held in order, floating in a "sea" of free electrons. If a piece of metal is hit with a hammer, the atomic cores will just move to a new place, and the electrons will fill in around them. The metal is dented, but nothing gets broken!
Students generally find it difficult to learn science. Teachers and parents have experienced all of this: the science concepts, the scientific method, and the experience of mental strain. But why is it so hard?
We have a helpful answer. First - teachers have to know how teenagers think. Then - we have to re-organize our science teaching to match the student.
Do we want our students to adopt the reasoning that scientists do? Well, of course we do.
The first thing to recognize about rational thinking is that is not “natural,” except in its most primitive forms. Rational thinking is highly cultural. In order for a human being to become a reasoning being, the act of reasoning must be learned, and sustained, in a way that is similar to the way one learns a language. We acquire language (and reasoning) by imitating our competent speakers and thinkers among our family and community. We become competent at language (and reasoning) by practicing, thousands of times, in everyday situations. And we become expert at language (and reasoning) by studying them explicitly.
Science, of course, is a discipline which requires a capacity to reason effectively. So… if a young person is attempting to learn science, that person must simultaneously learn how to reason.
But this brings us to a very important educational problem. Children do not find reasoning easy to do, or easy to learn. This difficulty is dissected in Daniel Kahneman’s book “Thinking, Fast And Slow”. Kahneman points out that we possess two quite distinct modes of thinking: Rational thinking, and intuitive thinking. They are quite different, as summarized in the table below.
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Intuitive Thinking
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Rational Thinking
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Fast
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Slow
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Easy – little energy required; faint evidence of raised glucose / oxygen consumption
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Difficult – takes a lot of biological energy, high glucose / oxygen consumption
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Occurs almost without effort
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Requires intense effort to push to a conclusion
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Pleasant – ends with very positive feelings
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Unpleasant – evokes strong feelings of stress
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Positive facial expressions: raised eyebrows, relaxed smile, open eyes
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Negative facial expressions: forehead frown, downturned mouth, squinted eyes
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May be impacted by senses, but proceeds to conclusion without registering a disturbance.
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Easily distracted by senses. People close eyes, seek quiet place, still their bodies, etc.
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Quite convincing to thinker. Feels “right.” Seldom followed by spontaneous resort to rational confirmation or disconfirmation.
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Not always convincing to thinker. Often followed by appeal to intuitive thinking to confirm or disconfirm rational conclusion
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Brain activity is global, includes more frontal cortex, less language, motor planning centers
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Prominent brain activity in language centers, motor planning centers in brain
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Associative reasoning: Given an input, neurons seek associated memories, feelings, instances, etc. and aggregate them toward a largely confirmatory conclusion.
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Differential reasoning: comparing parallel situations, comparing statements with recalled facts, limited number of operations, looks for nature of differences, etc.
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From Kahneman, “Thinking, Fast and Slow”
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- What are the takeaway points here?
First – One goal of science instruction is student competency in the second kind of reasoning - rational thinking. And adolescent human brains can be expected to avoid rational thinking, thus making student competency a very challenging task. Any curriculum that teachers create must directly address this difficulty.
Second – Intuitive thinking interferes with rational thinking. Faced with a lab setup or a textbook problem, a student is more likely to grasp for meaning using intuition, than to force his brain into rational mode. Intuitive thinking can easily disrupt the student’s effort at rational reasoning. Any curriculum that we design must directly address this likelihood.
Third – Science is a physical. It deals with real things in the real world. Students’ intuitive thinking about the real world takes place in the same mental space that governs their own physical movement in the real world. This mental space is called the “body-schema” by a number of researchers. Based upon my own observations, I believe that high school students use a small number of predictive / explanatory schematic strategies to guide their intuitive thinking as they attempt to make sense of an unfamiliar physical situation. When we plan science curriculum, we must anticipate that students will use “body-schematic strategies” to make sense of our instructions.
The IntuitivScience curriculum materials are designed with these three things in mind. Follow along. I will develop these ideas in future blogs.
The Bohr-Rutherford model is a high school staple. But does it help students learn real chemistry?
The BR model of the atom was designed in 1913 by combining Rutherford's nuclear model with Bohr's wave model. While it was insightful at the beginning of the last century, the BR theory was out-of-date by 1925. Yet it first appeared in high school textbooks between 1955 and 1965. Since then, no one has removed it. Why not?
We all agree that Teachers like it - it's easy to design highly focused exercises. Students like it - it's predictable and easy. Administrators like it - it's easy to generate standardized test questions. But apart from standardized testing, how can a high school student use the BR model?
Real science is concerned with predicting and explaining real world events. Can students use the Bohr model to predict the real properties of sodium? Its soft, shiny, metallic appearance, its chemical activity with water, and its basic behaviour? No! Can students use the Bohr model to explain the chemical properties of chlorine? Its non-metal appearance, its binary molecular structure, its reactivity, and its acidity? No - the Bohr model can't do any of that!
To a high school student, the Bohr model has virtually no predictive or explanatory properties. Students cannot use it unless an expert, a teacher, shows them how to crudely explain only two things: ionic and covalent bonding. Even then, the student must use the interpretive framework provided by the teacher, a framework that is much more elaborate than the model itself, and a framework that is not available to the students themslves. The students are not, by themselves, able to come up with "full octets" or "stable octets" or atoms "wanting" electrons, or atoms "needing to donate" electrons.
Pedagogically, the BR model of the atom is a fail. Students cannot build upon the model predict anything more than the teacher demonstrates. Students cannot use the model in any real scientific way!
What can teachers do about it? Teachers must always occupy two roles, and to play both roles simultaneously. Science teachers must be expert at science, and also expert at learning theory. So you, as a teacher, must consider two things.
As scientists, teachers know that the Bohr-Rutherford model is only a representation. A picture. Like any good scientist, when our scientific model fails, we must modify the model on scientific grounds.
We are both scientists and teachers. When teachers change a model, we must also modify the model on pedagogical grounds We must make the new model suitable for young learners.
If the new model is successful, it must be observably better at making scientific predictions, and more readily learned by the student.
I invented the Ross Model of the atom specifically as a pedagogical model of the atom - a scientifically powerful model that is easy for high school students to learn. In the next few entries, I will outline what the Ross model looks like.
