Lots of scientists have tried to figure out what our smallest building blocks look like.  It is not easy.  Atoms are so small you cannot even see them with a microscope.  We can only study how they act and then try to guess what they look like.  There have been some people who have come up with a picture of an atom that we think is pretty close to what they might really look like.  But they could not have done it alone.  Sometimes figuring something out happens in small steps.  It's kind of like someone loosening the lid on a pickle jar so another person can open it.

When working with things so small that we cannot even see them, all we can do is come up with a model of what it could look like.  A model is an example that's built to look like the real thing and helps us to get an idea of what something looks like.  In science, we use models to help us understand how something looks or works.  You might have seen a model that shows how the planets look as they move around the sun.  Most of the time, models are smaller than the thing they are showing.  But with an atom, any picture we make has to be MUCH bigger in order for us to see it.  It also has to look like something we, as people, know in order for us to understand.  As you will find out, our building blocks are not easy to pin down.

For a long time, people thought atoms were like a "plum pudding."  Think of a jelly with pieces sprinkled in it like raisins.  Then, in 1915, a scientist named Ernest Rutherford came up with a model for the atom that was a lot different than anyone had ever pictured.  Rutherford's model showed that the smallest building block had to have most of its stuff in the very middle with just a few things spinning around the outside.  No more pudding.  Sorry, everybody.

An atom that looks like plumb pudding? I don't think so.

That's right, instead of being stuck like raisins, most of the parts were spinning around the middle.  To orbit means to move in circles around one point.  This let Rutherford build a picture of the atom you know today.  It looks like a sun with planets spinning around it.  It was not exactly right, but this idea helped the next big idea come along.  The lid was now loose.

Rutherford's atom looked like today's atomic symbol.

That next big idea came from a man named Niels Bohr.  He figured out that if parts were just spinning around the atom, they would fall into the middle over time, and the whole thing would die.  So Bohr said that these parts had to move in fixed paths around the middle.  In Bohr's model, parts move in circles around the middle, each circle bigger than the last.  They cannot move out of their path like planets can.  If the atom ever added or lost energy, then the electrons would jump to another larger or smaller circle that goes around the middle part.  Not move, not skip, but just be there in a way we still do not understand.  Unless . . . you do.  If yes, good.  We could really use your help on this one.

Bohr saw atoms jumping from one circle to the other. I think I'd rather jump rope.

Great ideas do not always happen in leaps.  They happen in small jumps.  When Rutherford came up with a new idea of the atom with parts that circles around it, it was not really right.  But that idea helped Bohr come up with his own idea.  Now we have a pretty great idea of what the atom looks like.  So if you ever get something that is kind of right but not really right, don't feel bad.  You may have helped someone else take it the rest of the way.  It's like you got the lid on the pickle jar nice and loose.


Abyss.  "Bohr Atomic Model"  UOregon, 2009.  <http://abyss.uoregon.edu/~js/glossary/bohr_atom.html>

PBS.  "Bohr and Rutherford Describe Atomic Structure"  PBS, 2013.  <http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html>

Science Kids.  "Ernest Rutherford Facts"  Science Kids, 2013.  <http://www.sciencekids.co.nz/sciencefacts/scientists/ernestrutherford.html>

The Science Classroom.  "Niels Bohr"  The Science Classroom, 2011.  <https://thescienceclassroom.wikispaces.com/Niels+Bohr>