From: Roy Mayeda (roy_mayeda@isd743.k12.mn.us)
Date: Tue Dec 03 2002 - 08:59:44 PST
Date: 03 Dec 2002 10:59:44 -0600 Message-ID: <974274334roy_mayeda@isd743.k12.mn.us> From: Roy Mayeda <roy_mayeda@isd743.k12.mn.us> Subject: Re: pinhole compounds ... pure substances?
Sue,
Yes, they intend the term "particle" to mean basic unit of that material. A pure substance is one which has particles which are identical, and can't be separated by physical methods (without rearranging any chemical bonds).
George,
Yes, there is a little confusion generated by your statement. I think the basic reason that we run into this problem is that we are talking about different categories as if they are the same. (Students often relate element-atom-pure substance and compound-molecule-mixture.) These groupings are not the same, though there is considerable overlap in some of the groups. The basic problem with what you are saying is the statement regarding most elements having "molecules" of only one atom. Molecules have two or more atoms (of which element is irrelevant) bonded together. I know it also depends on the grade level at which you are teaching. I know that in lower levels, I teach that all compounds are formed of "molecules," but at higher levels we distinguish between molecular and ionic compounds. Just depends on how important this information is to the kind of understanding that you are trying to achieve.
I try to handle the groupings of matter regarding particles in this way (not that it's correct, but it has been useful in my classes):
Ways to group matter:
1) Pure substance vs mixture
Pure substances can't be separated by physical methods (eg. distillation, filtration, chromatography, etc.) while mixture can be separated without changing the chemical properties of each of the components. -- this last bit gets tricky to explain, especially at lower levels.
2) Atoms vs. molecules
Atoms are particles which are not bonded, and so can't be broken down by any chemical means. Molecules, whether made of one element or multiple elements, can be separated into individual atoms.
3) Elements vs. compounds
Elements contain only one "type" of atom. They can be found as individual atoms, or as molecules (N2, H2, O2, etc.). Compounds must contain at least two different "types" of atoms, connected by a chemical bond. (In general science we leave it at that. In Chem, we go on to look at ionic and molecular compounds, and the range of those characteristics based on electronegativities.)
It's hard to know how to present a lot of science material, because you want to generate understanding as well as stimulate independent thinking. We as science teachers usually know that a model is just that, and are not terribly confused if the model breaks down in other situations. Students sometimes lack that skill (sometimes this is a good thing!) and are confused by our explanations. No matter what explanation is given, the immortal words of Paul Doherty still ring true ... "But it is more complicated than that ..."
Hey, we're up to a tropical 10 degrees F! Hope my "ice garden" doesn't melt! :-)
Roy Mayeda
Sauk Centre HS
Sauk Centre, MN
("We're in the middle of Minnesota")
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