 Hello, I'm Kevin Conley from Foresight Tech, and I'd like to give you another lecture relating to nuclear chemistry. In this case, another example from nuclear equations that you'll be working out in your chemistry classes. This is a somewhat advanced example where you have to find not an unknown product, but you have to find an unknown reactant. This is very much like the previous lecture. The only change has occurred here in step four, where instead of trying to find an unknown isotope, we're looking for an unknown particle. The problem in this case is to write the balanced nuclear equation for the bombardment of aluminum-27. This will be the mass number because of course aluminum has its own inherent atomic number with a small particle, and that's probably going to be one of the alpha-beta gammas of the positrons, to form a sodium-24 and an alpha particle. So the alpha particle is going to be one of our products. The first thing to do is to write the incomplete equation. We have most of the information already. We have aluminum with a mass of 27, and if you look on the periodic table, you will see that aluminum's atomic number is 13. We're adding in an unknown particle that will probably be for bombardment reaction of some type, and the reactants then will include sodium, we find the 11, from the periodic table, and also an alpha particle as prescribed by the problem. The second step then is to determine the atomic number of the missing isotope, or truly the unknown particle as it should read right here. Well, the atomic number is going to be 13 plus some unknown z is going to be equal to 11 plus 2. So the atomic number 13 plus 0 is going to give us 11 plus 2, so the atomic number is going to be 0. The resulting particle won't have a charge, so you might want to think, alpha-beta gamma positron, which one of those doesn't have a charge? That's where my mind's headed. The next thing then is to determine the mass number of the missing isotope. Here we have 27 plus a, the mass number, equals 24 plus 4, so we have an a equals 1. Now I thought we were going to get some type of variation that was going to have, I was looking for a gamma particle, but this can't be a gamma particle because gamma particles don't have charge. I mean gamma particles don't have mass, so this can't be a gamma. So determine the unknown particle. Well, what do we know that has mass but no charge? That would make it a neutron. So let's put these together to write the balanced equation. We get aluminum plus a neutron for neutron bombardment is going to give us sodium plus the alpha particle. By checking our math, we simply see that 13 plus 0 equals 11 plus 2, check, and 27 plus 1 is 24 plus 4, 20 end of both sides, check.