how do chemists know what an atom looks like?

Question

while we know that water is H2O, how is it that we are so sure that it looks like three circles connected by two bonds of varying strength? how is it that chemists can be so sure about the structures of most molecules, and the innards of an atom? since you can't take a picture, you must guess, right? then why is it always taught with such certainty and authority?

Answer 1

Those are just diagrams, they're like blueprints of a house. They are not meant to be photorealistic. Photos have been taken though, with electron microscopes.

Answer 2

This is a big deal in chemistry and there are several ways to do this. It's pretty advanced stuff, though.

You can shoot x-rays at the molecule, and take a picture of the scattered x-rays after they hit the molecule. The way the molecule scatters the x-rays in a pattern depends on its' shape. It's how they found out the DNA molecule had a double spiral shape.

Another is theoretical, but it works for a lot of things (like the water molecule). There are a specific number of active electrons (the "outer shell" or "valence" electrons) for any atom. You can draw a molecule and can figure out how some of them form bonds with each other. Some are left over and pair up. The picture you get is called a "Lewis dot structure". When it's all done, all those active electrons, being negatively charged, repel each other and try to get as far away from each other as possible. You can figure out the shape that lets them do that. It's call the VSEPR method, Valence Shell Electron Pair Repulsion.

Here's a website that talks about the last method, in chapters 4.7 and 4.8.

http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter4section7.rhtml

This method is taught in first year college chemistry courses, maybe some high school courses, too. The best source of information would be a college chemistry textbook, although you can Google "Lewis dot structure" and "VSEPR" for some.

Shape is really important. The chemical reactions that make our bodies go depend very much on the exact shape of the chemicals that react together. So chemists work hard to determine shapes.

Answer 3

Years ago scientist using very powerful electronic microscopes were able to go into atoms and spell their names with sub atomic particles. They know exactly what will happen when two pure hygrogen ant one pure Oxigen meet with correct surroundings energy. The problems come from not using pure elements and getting correct surrounding energy. Don't want to over simplify, but if you keep studying your lean basic laws that make it simple.