Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Gosseyn on March 10, 2009, 05:39:44 PM
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I would like to know if the largest elementary molecule (one that is not a composite of other molecules) is smaller than the smallest colloidal particle. I'm saying that the colloidal particle would be about 1,000 times larger. Is that correct? If not, does anyone know the figure? Thank you.
Gosseyn
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Particle size
less than 10-9 m 10-9 – 10-6 m greater than 10-6 m
homogenous mixture colloids non-homogeneous mixtures
That looks terrible, but it's a direct cut-n-paste from the wikipedia colloid article, which has the data in a very nice table. And more useful info for you, besides.
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Particle size
less than 10-9 m 10-9 – 10-6 m greater than 10-6 m
homogenous mixture colloids non-homogeneous mixtures
That looks terrible, but it's a direct cut-n-paste from the wikipedia colloid article, which has the data in a very nice table. And more useful info for you, besides.
Assuming that is right, and if I am reading it correctly, then saying that the smallest colloidal particle is about 1,000 times larger than the largest elementary molecule would be about right, since the homogenous mixture is less than 10 to the minus 9. Does that make sense, or am I off about that?
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Particle size
less than 10-9 m 10-9 – 10-6 m greater than 10-6 m
homogenous mixture colloids non-homogeneous mixtures
That looks terrible, but it's a direct cut-n-paste from the wikipedia colloid article, which has the data in a very nice table. And more useful info for you, besides.
Assuming that is right, and if I am reading it correctly, then saying that the smallest colloidal particle is about 1,000 times larger than the largest elementary molecule would be about right, since the homogenous mixture is less than 10 to the minus 9. Does that make sense, or am I off about that?
By the way, I'm not taking a chemistry class, and this was not a question on any test. I just want to know because I'm writing a brief history about colloids and want it to be accurate.
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| | | Particle Size |
| less than 10-9 m | | 10-9 to 10-6 m | | greater than 10-6 m |
| homogenous mixture | | colloids | | non-homogenous mixture |
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So the smallest colloidal particle would be about 10 times larger, not 1,000 times larger, than the largest elementary molecule. I hope I have it right now; can anyone confirm?
This is how my modified essay reads now: "At the time when the colloidal particles began to be studied in earnest, they were too tiny to be seen through the most powerful optical microscopes yet were about 10 times larger than the largest elementary molecule. They existed in a kind of twilight zone between the two domains; but it was known that all life was manifested in the colloidal state. That was the thought that intrigued."
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So the smallest colloidal particle would be about 10 times larger, not 1,000 times larger, than the largest elementary molecule. I hope I have it right now; can anyone confirm?
This is how my modified essay reads now: "At the time when the colloidal particles began to be studied in earnest, they were too tiny to be seen through the most powerful optical microscopes yet were about 10 times larger than the largest elementary molecule. They existed in a kind of twilight zone between the two domains; but it was known that all life was manifested in the colloidal state. That was the thought that intrigued."
Looks like I'll have to change that. In Colloid Chemistry (1929), there is a table that lists the approximate size limits of molecules as "0.2 to 5 uu," and primary colloidal particles as "2 to 20 uu," so there appears to be an overlap. Can anyone tell me what the symbol uu stands for, and how to pronounce it? I know that A.U. stands for Angstrom Unit. The uu symbol has the front part of the u a little different.
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I think what you may be seeing is um, properly written as µm*, called micrometer, or informally, micron. It is a unit of size, one millionth of a meter. I hope, with all your reading, you're beginning to realize that there is not a perfect, accurate, definition for when colloids end and solutions of molecules begin. Rather, it's about the properties of the molecules that keeps the particles suspended, when another molecule of the same size would precipitate.
*depending on your computer system, you may not be seeing that character properly. It is the Greek letter mu.
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I think what you may be seeing is um, properly written as µm*, called micrometer, or informally, micron. It is a unit of size, one millionth of a meter. I hope, with all your reading, you're beginning to realize that there is not a perfect, accurate, definition for when colloids end and solutions of molecules begin. Rather, it's about the properties of the molecules that keeps the particles suspended, when another molecule of the same size would precipitate.
*depending on your computer system, you may not be seeing that character properly. It is the Greek letter mu.
Thanks.
It is definitely not the micron, unless it's an old-fashioned way of saying that as this is from 1926.
It says "X 10,000 = µ"
then "X 10,000,000 = µµ"
The A. U. = "1/1,000,000 [µµ]" the µµ is at the dividing line.
From what I am reading maybe surface area (and electrical charge) of the particles is one of the keys to colloidal behavior. Just to be clear, µ is pronounced, "mu"?
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Yep. That's more like "mmmew" like a cow with a French accent would say. Calling small things "micron-sized" was an old way of describing small things, before SI units standardized them. You may have another, old unit there. Or maybe it is a typo.
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Yep. That's more like "mmmew" like a cow with a French accent would say. Calling small things "micron-sized" was an old way of describing small things, before SI units standardized them. You may have another, old unit there. Or maybe it is a typo.
Thanks, oh, I see, M is the uppercase Greek, the u is the lowercase. Likely not a typo, as it shows up in multiple articles in the book from international contributors. I wonder if using it that way was a German custom or something, as the editor, Jerome Alexander, came out with an earlier book on colloids by a German scientist.
Gosseyn