GCSE Atomic Structure

You've heard of Hiroshima and Chernobyl, you've heard of this mysterious powerful thing called radioactivity.  You know that huge quantities of energy can be released from small masses of uranium. And this can be of great benefit to mankind but also vast destruction.

You'll perhaps be quite comfortable with the Bohr model of the atom.  Protons and neutrons sitting pretty in their nucleus, electrons languidly orbiting around it.  It doesn't look like much is going on at all, nothing exciting certainly.  And you'll perhaps be happy with the idea that the elements in the periodic table are fixed, that gold will always be gold and copper will always be copper.

You'll perhaps be happy with the ideas from chemistry that electrons are donated our shared between atoms, and that that is how atoms bond into molecules, and how energy is taken in our given out in chemical reactions.  But in physics we're far more interested in the nucleus than these electrons in their shells, or energy levels as we prefer to talk about in Physics.

You see the nucleus is where the majority of the energy is!  The nucleus is an incredibly dynamic thing, with all this jiggling motion, all  this excess energy just bursting to get out.  And it's when this nucleus changes that all that energy is released.

Think about a nucleus carefully, there are protons all positively charged, electrostatically repelling one another, and neutrons doing nothing to stop this, so they want get away from each other… so why do they all stick together?  Well there must be another force holding them together.  And it must be very strong.  We call this force the strong nuclear force.  Imaginative right?

There's a constant tug of war between these two forces in the nucleus, and at any moment the nucleus can just kick out some energy or a particle, which we call a decay.  We cannot predict when it's going to happen, we can just say the nucleus is more or less stable, so more or less likely to decay.

There's a kind of perfect balance of protons and neutrons where these two forces are most closely equal, and so when the nucleus will most stable.  If a particular isotope has too many or too few neutrons, it will be more likely to decay!  We call these isotopes radioactive isotopes.