Saturday, June 21, 2014

Atoms and Atomic Particles

I was just a boy when I first heard of atoms. I’m not sure how old I was. Older than 12 but probably younger than 14. I was sort of a science nerd … even back then. I was mostly interested in electronics at that point in my life. I had a subscription to Popular Electronics, and I was into things like ham radio and building various electronic gadgets.

I may have started with one of Isaac Asimov’s books on chemistry or atoms. I read a lot of Asimov in those days, both his science fiction and his nonfiction stuff, which was excellent and easy to understand.

So I knew about atoms and molecules and that atoms were made up of electrons that orbited around a nucleus and that the nucleus contained positive charged protons and neutral neutrons. I knew that electrons were the particles that made up electricity and that formed chemical bonds and that the nucleus was the place where fission occurred in atom bombs and nuclear power plants.

I knew that electrons were very light relative to the particles in the nucleus (called nucleons). In fact, the proton weighs (an imprecise term when atoms are concerned) about 1,000 times as much as an electron and a neutron weighs just a tiny bit more than a proton.

(Weight really is the result of the force of gravity on a property called “mass.” Weight would be different if gravity was different. For example, things weigh less on the moon. A metric unit for mass is the kilogram or one thousand grams, which has the abbreviation “kg.”)

There is another unit for mass, called an electron volt (eV), that scientists use when talking about small things like protons, neutrons, and electrons. An electron volt is actually a measurement of energy, but scientists can get away with using it to measure mass since mass and energy are related by Einstein's famous equation, E = mc2. So, in terms of MeV (Megaelectron volts, 1 MeV = 1,000,000 eV), the mass is shown in the following table.

Here are the details, just in case you’re into the numbers.

Mass of Atomic Particles

Particle Relative Mass Kilograms MeV
Neutron 1 1.6749286*10-27 939.56563
Proton 0.99862349 1.6726231*10-27 938.27231
Electron 0.00054386734 9.1093897*10-31 0.51099906

I never tried to memorize these numbers other than the fact that the neutron is over 1,000 times heavier than an electron. In fact, it is about 1,800 times as heavy. (Therefore, almost all of the mass of an atom is concentrated in the tiny nucleus and atoms are mostly empty space.)

You will notice, however, in using the convenient eV values that a proton and a neutron weigh in at almost exactly 1 GeV or Giga-Electron Volt. That’s a thousand million which some — at least in England — call a billion. (Here in the US we consider a billion to be a million million, at least for purposes of Federal budgets.)

(Giga is now familiar to most nonscientists because of the size of modern personal computer disk drives have grown from megabytes to gigabytes and even to terabytes.)

Getting back to my story, after studying the mass of the particles, I got an idea. It looked to me like a neutron might be a proton combined with an electron. After all, the plus and minus charges would cancel yielding the neutral charge of the neutron. So I did the math.

Proton = 0.99862349
Electron = 0.00054386734

So I added them:


Close, but not exactly 1.0. I assumed the missing mass was used up in energy holding them together. At least it didn't add up to more than the mass of the neutron, which I would not be able to explain.

(I didn’t really understand Relativity all that well before Junior High, but that wasn’t a bad guess about mass becoming energy. That's what makes atom bombs go BOOM! The mass of the fission products is slightly less than the original mass and that tiny amount of mass is converted to energy as heat and light — with a c-squared multiplier, and "c" is a very big number. So just a little bit of mass and you get a real big BOOM.)

In fact, at the end of the 19th century, when scientists were just discovering the makeup of the atom, it was supposed that the nucleus contained protons and electrons, with an overabundance of protons supplying the positive charge. Early on they didn’t know much about the nucleus other than the fact it attracted electrons and it was very dense.

Although they were unknown back in the fifties, we now know that protons and neutrons are make up of more elemental particles called “quarks.” Electrons, however, appear to be elemental particles and there’s nothing smaller “inside.” So my guess wasn’t all that crazy.

That is how science is advanced. Someone, maybe a small boy, has some crazy idea — called a “theory.” Then the experimentalists go to work to try to confirm or disprove the theory. My theory was actually disproved in the early twentieth century. But I didn’t know that when I was only 12. I started learning these more complex and detailed facts about atoms when I got to college. My simple view worked all through High School.

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