Question for a Chemist

[Shooby]

Hello All,
My math professor told the class that we've never actually seen inside of an atom, only the surface of an atom. My question is:
How do we know that there are electrons spinning in specific multiple orbits, around a nucleus, containing protons and neutrons?

I know that the things that I learn in chemistry class must be true. We use our knowledge of atomic particles everyday in industry,etc. And the results are always the same, based on the periodic table,etc.
It just seems very weird to me that we know things without ever having seen them.

Steve

[Neuge]

It's very hard to explain in pseudo-layman's term, certainly beyond my ability (I'm a chemical engineer, not a chemist). You almost have to be familiar with at least the basics of quantum and statistical mechanics. I really don't know what to tell you besides go check out a good Physical Chemistry textbook from the library.

There are various experiments that have 'proved' that atomic nuclei and electrons exist (Milikan's oil drop experiment, Thompson's cathode ray tube experiments, the gold reflection experiments (I can't remember their names right now), etc..), but to really understand the framework of how these construct an atom and why, you have to understand a ton of quantum theory.

[Metric]

I think your professor is using the word "seen" in an overly literal way (probably on purpose, to get you thinking in exactly the way you are). We can observe some process that involve interaction with the nucleus or tightly bound electrons and deduce many of their properties.

[MikeSmith]

If we dont then i guess i and all pharmaceutical companies are just throwing darts in the synthetic lab. Look at your medicine cabinet chief, all those were made on the basis of chemistry theory.

[ChrisV]

Hi Shooby,

It has been known for a long time that atoms consisted of electrons plus some positively charged matter. There are any number of ways to show this by knocking electrons out of the atoms. The original experiment that showed that the structure of atoms was a very small, positively charged nucleus surrounded by orbiting electrons was the Rutherford experiment. Rutherford (one of his students, actually) fired small, positively charged particles called alpha particles at thin gold foil and measuring the angle of deflection. He found angles of deflection much greater than had been anticipated, indicating that some of the particles were colliding with (or passing very close to) a very small, very positively charged mass.

Since then, physicists have determined what the nucleus is composed of by smashing particles into atomic nuclei at high speed and observing the debris.

What your teacher meant is that if you try to observe an atom, by say reflecting photons or electrons off it, all you see is the outer electron cloud. To see a nucleus, you have to destroy the atom by smashing it to pieces.

[Shooby]

To All who responded,
Thanks for your info. I don't really understand any more of the specifics, but I see now that we do know this stuff, just not the way I thought we would. BTW, I find it interesting that I recieved a better answer here than I did on chemical forums.com Kind of ironic.
Shooby

[flipdeadshot22]

[ QUOTE ]
To All who responded,
Thanks for your info. I don't really understand any more of the specifics, but I see now that we do know this stuff, just not the way I thought we would. BTW, I find it interesting that I recieved a better answer here than I did on chemical forums.com Kind of ironic.
Shooby

[/ QUOTE ]

you probably didn't get a great answer from chemical forums.com since this is a question better suited for a physicist.

[latefordinner]

http://www.discovery.com/area/skinnyon/skinnyon980109/skinnyon.html

[Shooby]

Cool, thanks for the link.
Shooby

[MrMon]

First off, the idea that electrons are in orbits spinning around the nucleus like little planets is not really true, but it provides a useful model that is easy to understand. The reality is that the electrons exist in a "cloud" at different energy levels and where "it" is in that cloud at any given time is rather random. The quantum model of the atom is just too odd for most students to comprehend, so we stick with the mini-solar system model for lower level science classes.

But you original question raises a bigger question that is actually the subject of a lot of discussion in the philosophy of science - namely, do theoretical objects exist and are they different from observable objects? The possible different answers to this question lead to some surprising results, and if you extend it as far as the postmodernists have, you skate right over the edge of a cliff. It's an interesting subject that quickly gets rather deep, and there really is no answer that everyone accepts. But for the sake of sanity, most people never even bother contemplating it in the first place.