how do you make a3D model of an atom?

Answer 1

Ping pong balls make great nucleids (neutrons and protons). Paint the protons red and the neutrons black, for example. Use super glue (or similar) to glue them together. (Alternatively you can use double sided adhesive tape, but that won't last as long.)

Keep it simple. I wouldn't do anything more than an H or He atom. Even ping pong balls will end up with a very big model at the high end of the table of elements.

Then to be consistent with the latest models (not the Bohr model), use thin (translucent) gauze or some similar material to show the electron probability cloud around the ping pong ball nucleus. (You'll have to scale the expected value (aka orbits) because the electron clouds are relatively quite far away from the nucleus.) Thin, stiff wire, can be used to standoff the gauze at the proper distance from the ping-pong balls.

Answer 2

Usually with the foam craft shop balls. It really depends on the model you are modelling. Is scale important? I have had student build pretty cool ones like mobiles with spinning orbitals that give the impression on "randomness". The cloud model is a little more difficult. If this is for a class project try to think of the way other students won't think of doing it. Vary your materials. Aluminum foil balls colored with permanent marker make nice electrons.
The important thing is that you have the correct number of each particle for the element you are showing. Also, make sure all neutrons are the same, protons the same, and electrons the same.

Answer 3

Use a computer chemistry program. Some are very straight-forward and there are also some interactive websites where you can do it. I suggest you google it.