 The topic of this video is nuclear chemistry, in particular an introduction as well as history. So in this video you'll be given a general introduction to the concepts of nuclear chemistry, as well as a timeline from the beginning of the discovery of the nucleus up until the present day. So first of all, there are a number of subatomic particles that make up the atom. The atom is made up of the cloud of electrons on the outside, which is where virtually all chemistry does occur, but inside the nucleus we do have the protons, which balance out the charge of the electron and tell us which element we're actually dealing with, and also that there are the neutrons that hold the nucleus together. If, for example, in helium we simply had two protons to balance the two electrons on the outside, why would the protons want to stay together if they both had positive charge? They would repulse each other. With two protons and two neutrons they'll be holding each other together more stably and the neutrons hold the nucleus together. We've also studied the concept of isotopes. Let's take a look at carbon in particular. Carbon is made up of stable isotopes, a number of them, two and three are natural in particular, but carbon has exhibited a number of isotopes all the way from having eight constituents in the nucleus up to 22. Recall, in every case though, carbon will have six protons in every one of these cases. If it had five protons it would not be carbon. So when we take a look at carbon 12 it really is six protons and six neutrons. Carbon 12, the foundation of the atomic mass unit, is very stable and natural, and that is the common constituent of the carbon that we encounter every day. Also the carbon that we encounter every day has elements of C13 in it. Both of these are naturally occurring and they're also stable. What also occurs naturally though is carbon 14. Carbon 14 is a naturally occurring isotope of carbon but it is unstable. It is slightly unstable. Every 5,700 years half of your amount of carbon will disappear. This can be very useful for a number of applications as we'll see later. Artificially the most stable nucleus of carbon that can be synthesized is the C6. It is a half-life of 20 minutes. This is an example of how the half-life, which we'll get to much later, or the stability of the nucleus depends greatly on which isotope we're dealing with. They can be very, very long and also somewhat short. The colors here have indicated whether or not the isotopes are stable or unstable. When you have an unstable nucleus such as C14 or C11, these isotopes will decay. They will decay into some other isotope that is in fact stable. But they may go from being carbon, for example, to go back to be boron. They may actually change the element that they are when they lose radiation. So any unstable isotope will eventually undergo a radioactive decay. In the process of undergoing a radioactive decay, they will emit radiation. Radiation consists of a number of different forms and we will get to those in subsequent videos as well. One thing to keep in mind when we're considering radiation is that radiation occurs in particles. Sometimes these particles are just pure energy, in which case we will call them photons. But sometimes it's just pure energy that comes off with no mass. Sometimes the radiation is a particle that does have mass and will give you a name for that particle. So you might want to keep in mind sometimes that the particles that come off of radiation may just be energy with no mass and sometimes they may be a chunk of mass that does come off with energy. To give you a bit of history concerning the nucleus, let's take a look at some of the events and some of the activities that have occurred. First of all, about 1900, Henry Becquerel and Marie Curie were the first ones really to notice radioactive decay and what was taking place inside the nucleus. In a previous video we have demonstrated as well the work of Henry Mosley as well as Rutherford in their discovery of nucleus around this time. A while past and then during the period of time between about 1939 and 1944, nuclear weapons were developed. And this is of course a very important development. Afterwards in the 50s, archaeology was greatly promoted by the use of radiocarbon dating. Many things in archaeological digs were dated according to radiocarbon dating. Also in astronomy, great strides were made in understanding stellar evolution which is why some stars are bright, why some stars are very dim, why some stars pulsate and why some stars may have a color in particular. And then also electricity, this comes about because of the nuclear reactors that began to be constructed during the 1950s and many, virtually all of those are still in use today. In 1960 particle physics became an important field of study where atoms of carbon for example would be smashed together with great amounts of energy and then the results would be splattered everywhere and the results of what would come out would be protons, neutrons, electrons, different isotopes but also very different types of particles. So the very inner core of that nucleus was studied in the 1960s. In 1979 there was an accident which was a very mild accident at Three Mile Island in Pennsylvania which you may be interested in looking into. Also in 1986 there was a very significant accident that occurred in Chernobyl Ukraine which is also worth your time to look into. There of course was one that occurred in Fukushima just a few years ago and there are a number of cases where uranium is stored improperly that cause elevations of radiation to rise that aren't quite dangerous but great care needs to be taken in managing these isotopes. Finally in 1990 in medicine versions of positron emission tomography, PET scans and different scans like that began to be available for medical applications and these are very advanced applications that have made great strides for medicine. Thank you for your attention.