[Uri]

A question for chemists...

How do you know how a substance looks like, feels like and smells like in real life from a drawing of it's chemical structure alone? And more importantly how do you know it vice versa, the chemical composition of a substance from how it looks and feels like in real life?

For example, trifluoroacetic acid, how do I know what it looks like in real life from a chemical structure drawing like this?

Also how were the chemical elements and the periodic table discovered back then without the aid of powerful microscopes and spectrscopes like we have today?

[Uri]

I would also like to ask and I hope that I'm not repeating myself, back then how did they know that they discovered an element without a microscope which really shows them the chemical structure?

[Borek]

How do you know how a substance looks like, feels like and smells like in real life from a drawing of it's chemical structure alone? And more importantly how do you know it vice versa, the chemical composition of a substance from how it looks and feels like in real life?

In general - you don't. You deduce its structure from how it behaves reacting with other substances of known structure.

back then how did they know that they discovered an element without a microscope which really shows them the chemical structure?

Microscopes are of no use when it comes to discovery of an element and to check structure of the substance. Their magnification is much too low for that.

I think you should try to read some popular books on chemistry history, for sure some of them will show how it was possible to deduce information from the data that the scientists had available. Unfortunately, I can't suggest any titles; perhaps others will.

In general it is like with a giant, multidimensional puzzle - you know several pieces, you know several rules, and you have to combine elements in such a way that they fit. Throughout the process you discover new rules and you find out that there must exist new pieces, that you have not seen before. That's how every science works,

[Uri]

In general - you don't. You deduce its structure from how it behaves reacting with other substances of known structure.

So how was the very first strucutre discovered?

[azmanam]

So how was the very first strucutre discovered?

Through generations and generations of experiments.  The greeks thought there were 4 elements: earth, fire, air, and water (I am Captain Planet!) (http://en.wikipedia.org/wiki/Classical_element).  Before oxygen was discovered, chemists thought there was an 'element' of heat and fire called phlogiston (http://en.wikipedia.org/wiki/Phlogiston_theory).  It was contained in combustible substances and released upon burning.  They also thought light was an element.  In the 1700s and 1800s, elements started to be posited, but chemists thought simple compounds combined in a 1:1 ratio: that is, water was HO, ammonia was NH.  An element was taken to be a substance which could not be broken down any further by chemical means.  They were sometimes isolated by decomposition of compounds containing them.

Great question, no easy answer.  Start here: http://en.wikipedia.org/wiki/Chemical_element

[azmanam]

if you're still intrigued, check this book out of the library.  it's fascinating and a pretty easy read.

http://www.amazon.com/Chemical-History-Tour-Picturing-Chemistry/dp/0471354082/

[Uri]

In the real world we see the MACROSCOPIC properties of materials like color, smell, taste, strength, hardness, sharpness and also the PHASES of matter.

Chemistry deals with the MICROSCOPIC properties of matter which the people who work in the plastics industry, in the rubber industry, in the textiles industry and in the composite materials industry CANNOT see. We don't see the microscopic properties of matter in our daily life, we only see and sense the MACROSCOPIC properties.

That is not to say chemistry is crap but I think that the interpretation of chemistry of our world is not completely correct.

I studied cognitive science and especially cognitive linguistics and psycholinguistics and all I can say is that the interpretation of cognitive linguistics of our world is much better than that of chemistry but is also not complete.

Our world also involves interpretation and hence is quite different than the world chemistry, physics and biochemistry describe. Our world contains mental, linguistic and cognitive elements as well as matter and radiation.

Hence the interpretation and explanation of our world by physics and chemistry is in my opinion only good on paper or on the computer screen but in the real world or in our daily life it FAILS.

[DrCMS]

That is not to say chemistry is crap but I think that the interpretation of chemistry of our world is not completely correct.

What do you mean?

Hence the interpretation and explanation of our world by physics and chemistry is in my opinion only good on paper or on the computer screen but in the real world or in our daily life it FAILS.

Complete and utter rubbish written down by a fool who does not understand the real world.

What did you eat today? - Chemistry
How did you type that in to a computer? - physics and chemistry.
Ever taken any drugs or drunk alcohol? - chemistry
Drive a car flown on a plane? - physics and chemistry
synthetic fabrics - chemistry
dyed clothes - chemistry
plastic containers - chemistry
soap/toothpaste/detergents/shampoo - chemistry

The whole world relies on chemisry and physics to function.

[Uri]

Complete and utter rubbish written down by a fool who does not understand the real world.

What did you eat today? - Chemistry
How did you type that in to a computer? - physics and chemistry.
Ever taken any drugs or drunk alcohol? - chemistry
Drive a car flown on a plane? - physics and chemistry
synthetic fabrics - chemistry
dyed clothes - chemistry
plastic containers - chemistry
soap/toothpaste/detergents/shampoo - chemistry

The whole world relies on chemisry and physics to function.

That's wrong. Our world also requires language and symbolism to function. Our world also contains symbolic and linguistic elements as well as chemical and physical elements.

Those who work in the plastics or in the rubber industry have never seen a molecule, a compound or an atom in their entire lives. The only thing they do see and can work with is the MACROSCOPIC properties of matter that we see in our daily life. We don't see molecules, atoms or compounds in our daily life, we only see and sense the MACROSCOPIC properties of matter.

Chemistry is pretty much useless to us in ordinary life when only the macroscopic properties of matter play a role and of course: language, symbolism and drawings too!

[DrCMS]

The whole world relies on chemisry and physics to function.

That's wrong. Our world also requires language and symbolism to function. Our world also contains symbolic and linguistic elements as well as chemical and physical elements.

No I never said language and symbolism do not have a place in the real world they obviously do as we are using them to have this argument.  I was replying to your statement that physics and chemistry do not matter in the real world.  Which is so so wrong as to be laughable.

Those who work in the plastics or in the rubber industry have never seen a molecule, a compound or an atom in their entire lives.

Correct but we see the effect of them all day everyday.

The only thing they do see and can work with is the MACROSCOPIC properties of matter that we see in our daily life. We don't see molecules, atoms or compounds in our daily life, we only see and sense the MACROSCOPIC properties of matter.

Chemistry is pretty much useless to us in ordinary life when only the macroscopic properties of matter play a role and of course: language, symbolism and drawings too!

This just proves once again how little you know.  The macroscopic properties of a food or drug may affect how they appear but the chemical interaction you can not see determine how they interact with your body.

Just because you do not understand chemistry and physics does not mean they are not vitally important in the real world.  Before humans had language chemistry and physics still had meaning in the real world.

[renge ishyo]

The short answer for why we know what we know in Chemistry is that (for science in general) we do experiments that can test and disprove our ideas. This is what distinguishes it from other studies of thought which do not require that the conclusions be testable. For example, this statement "Our world also requires language and symbolism to function" may or may not be true. You can't test it. I can just as easily say that humans survived and functioned before they were able to develop languages, and cite fossil records that predate the early alphabets created by the early societies. Then you can counter by saying that maybe they did know language, but we just have no record of it. Then I can counter by saying non-human animals like bees can form functional societies without language so by analogy we should as well, and on it goes etc. etc. Who really knows the answer. Neither one of us can test any of this.

In contrast, if you stick an electric current through water you can isolate two gases that are always in the proportion of 8 parts of 1 gas to one part of another by weight. If someone comes up with an idea of "no no, it should be 5 parts to 1 by weight!",  well, we can safely say he is wrong because when we do the measurements over and over again we always get 8 parts of one to one part of the other by weight. So THEN we try to come up with ideas where we end up with 8 parts to one by weight. A bunch of ideas come out and then we do some other experiment where we get some other result and we check the new theories against that result. Some of these theories work with the new experiment, but others don't and get thrown out, and so it goes with more and more experiments until we narrow in on the answer. That's how science arrived at its more useful conclusions. If you are really interested in how we know what a molecule is, I recommend reading Issac Asimov's "A short history of chemistry". It will walk you slowly and gracefully (it is perfect for non-scientists) through those trials and errors so that you get a great feel for how we arrived at the conclusions (but quality doesn't come cheap, this book is still $80 on Amazon...).