Ye olde Bohr atom. It's crude compared to the best modern physics explanations, but it is an easy to understand approximation -- and it can make very attractive little spin toys. My daughter saw Thing 114247 and asked me to print some as a gift for her Physics teacher (spelling out P H Y Si Cs). However, 114247 uses pre-discovery names for four elements, is one-sided, chunky (slow to print), didn't have an integrated mount, and was likely to not spin freely... so I was inspired to create this better model.
This design is larger, but two-sided, prints faster fully assembled without supports, and you can turn the parts by simply blowing on it. It can be printed with an optional integrated hanger or stand. Here's a movie of the Si model spinning as a hair dryer is pointed at it from a foot away: https://youtu.be/Tz-r02JZf98
The atoms all print fully assembled without supports -- even the optional stand literally prints as an integral part of the atom. It prints well in PLA, but nearly any material should work.
There are short unsupported spans and there are tiny pads that need to stick precisely in position on the bed. The spans shouldn't be a problem, but you need to make sure everything sticks to the bed. Although a clean, heated, glass bed worked fine for me, consider printing on blue tape, using glue or hair spray, etc. to help things stay precisely in place during printing.
There really shouldn't be anything to clean up. That said, you might like to accent the text by painting it or coloring with a permanent marker. You'll also find that the joints tend to operate smoother after they've been worked more. Properly printed, you should be able to rotate any of the parts simply by blowing on them.