 Today on Flippin Science we're talking about isotopes. So what is an isotope? So an isotope is when we're comparing two atoms they have the same atomic number but they have a different mass number and the reason why they have a different mass number is because they have either more or fewer neutrons than a regular atom would have. So let's talk about hydrogen for example. So most hydrogen if we looked at the hydrogen nucleus there's a proton and then if we look at the electrons we've got one electron zooming around it like that. So that's the nucleus of a regular hydrogen. So we call that hydrogen 1 1. Okay so one is the atomic number one is the mass number. Some hydrogen has a proton and a neutron in the nucleus and again one electron flying around. So this has proton and a neutron so it has extra mass in the nucleus. The atomic mass of this will be twice as much because the mass of protons and neutrons around about the same. So this is hydrogen 2 and then we've got, we could have hydrogen 3. It's got a proton and two neutrons joined together and again still one electron at the top. So this is hydrogen 3. Okay so two neutrons one proton total mass of 3 because we've got three things in the middle and that's our three types of hydrogen. Now this is the most common and these two are fairly rare. The reason why these different isotopes of hydrogen are important is because they can be used for different things. They react exactly the same chemically because they have a single electron they are going to react the same way that all hydrogen does. But you're going to get different water molecules for example that have an extra neutron present. So we call that heavy water when there's extra neutrons because the water has more neutrons in the nucleus so overall you have heavier water. Heavy water is used in many nuclear applications. So each of these hydrants has the same number of protons in the nucleus. They all have one proton and because of that they'll react the same because they have the same number of electrons. But in terms of their mass that's different. So they have different physical properties they have a different mass because of the different number of neutrons present in the nucleus. We're going to have a look at some examples in carbon in a second.