1.3 What's Inside an Atom?

The atomic model we're going to be using for this course was developed by the renowned Danish physicist, Niels Bohr. His model consists of a central nucleus surrounded by a series of electrons. The electrons orbit the nucleus much like the Earth orbits the Sun. So in a way, atoms are like a smaller version of our solar system. We'll begin by looking at the nucleus.

There is a nucleus at the center of each atom. Since this course is about nuclear fission, I’m sure you've already figured out that, for this course, this is the part of the atom about which we will be the most concerned. It turns out that the nucleus of an atom consists of even smaller bits of matter. The bits of matter are called, conveniently enough, nucleons. For the purposes of this course, we’re really only going to concern ourselves with the two most important players in the nucleus, the proton and the neutron.

We'll begin by discussing the proton. As we'll learn later, protons are really the most important part of the nucleus. They give each element their character. As we said previously, all matter has two properties in common, mass and electrostatic charge. The proton has a mass of 1.00727 Atomic Mass Units and an electrostatic charge of +1.

The other resident of the nucleus which is important to us is the neutron. Neutrons are a bit bigger than protons and have a mass of 1.00866 Atomic Mass Units. Ironically, neutrons have no electrostatic charge. They’re neutral, like Switzerland, but without the tasty chocolate. As we'll find out later, even though they lack an electrostatic charge, neutrons are incredibly important to the fission process. Without neutrons, there would be no fission process and I wouldn’t be writing this text.

Lastly, there's the lonely electron. It orbits the nucleus and therefore is not considered a nucleon. While electrons are incredibly important when studying chemistry, they're fairly insignificant in the study of nuclear fission. The only thing electrons bring to the nuclear fission party is their electrostatic charge which is -1. In terms of mass, electrons are practically negligible, having a mass of 0.00055 Atomic Mass Units. Generally, we don't consider an electrons mass when discussing nuclear reactions. This table sums up the properties of the sub-atomic particles which we have discussed.

Before we go on, I want to take a minute to discuss the scale of atoms. Because they are so small, it's nearly impossible to visualize the particles we will be studying in this course. So let's put the atom into perspective. If the nucleus of the atom were the size of marble and we put that marble on the goal line of a football field, the outer edges of the electron orbits would be the other goal line. Now quantum physicists will argue about this analogy, but what do you expect from people who spend all day thinking and arguing about things they can't see directly. This information really isn’t germane to the course, but it's something cool to think about.