by Jason Amores Sumpter

all right, So now that we've covered the basics of the atom in this video, we're going to introduce isotopes. And so all atoms of the same elements are going to have the same number of protons. And that's because if you change the number of protons, then by definition you're going to change the element. And so once again, all atoms of the same element will have the same number of protons. However, all atoms of the same element do not necessarily have the same number of neutrons. And so the number of neutrons can vary between atoms of the same element. And this is exactly what leads us to this idea of isotopes. And so isotopes are defined as atoms of the same element that Onley vary in the number of neutrons. And so isotopes are always once again going to have the same atomic numbers. And that means that they're gonna have the same number of protons. And once again, that's because if you change the atomic number or the number of protons, you're going to change the element. And so all isotopes will have the same number, same atomic number or the same number of protons but once again they do not have the same number of neutrons. So that means that they will have different mass numbers, which recalled. The mass number is the total number of protons and neutrons, and the reason they have different mass numbers is because they have different neutrons. And so if you have varying number of neutrons, then you're automatically going to vary in the mass number. Now recall from our previous lesson videos that not only did we define atomic number and mass number, but we also defined the atomic mass, which is very similar to the mass number. But it's different in the fact that it is going to be the average mass of all of the isotopes that exist for, ah, particular elements. And so let's take a look at our example down below to look at the atomic mass of carbons three isotopes and so you can see that we're showing you the three isotopes of the carbon atom down below. The first one is here. The second one is here, and the third one is right here. Now, one thing to note about these three isotopes of carbon is that they all have the same exact number of protons. They all have six protons and that is once again going to be the atomic number. So they all have the same atomic number in the same number of protons as we indicated up above Now, also notice that all three of these scenarios right here also have the same exact number of electrons. Theological Tron also does not vary between these three scenarios. And so really, the Onley thing that differs between these three scenarios is going to be the total number of neutrons which we have here in the middle. Notice that when you count up the number of neutrons in the nucleus of this first one, there are a total of six neutrons. When you count up the neutrons here there are a total of seven neutrons. And when you count up the neutrons here there are a total of eight neutrons. And so once again, these three scenarios right here on lee differ from each other in the total number of neutrons in the nucleus. And that is what makes them isotopes, atoms of the same element that Onley vary in the number of neutrons. Now, if we wanted to calculate the mass number for each of these three scenarios, then we need to total up the total number of protons and the total number of neutrons. But once again, the total number of neutrons is going to vary, which means that the mass number will also vary for each of these isotopes. So if we want to determine the mass number for this first Adam, we take the total number of protons, which is six, and add that to the total number of neutrons, which is also six. And that gives us a mass number of 12. And so this is referred to as a carbon 12 Adam on. Once again, it can be abbreviated as this right here where the 12 indicates the mass number and the six indicates the atomic number or the number of protons, which does not change in all of these scenarios. Now, if we want to calculate the mass number of this second isotope once again, take the total number of protons. Add the number of neutrons, so six plus seven that gives us 13. So this isotope here is carbon 13. And so once again, we can put the 13 up above right here to indicate its mass number. And then, uh, if we wanted to do the same and calculate the mass number for this last isotope over here, all we need to do is some of the total number of protons, which is six plus. The number of neutrons, which is 86 plus eight is 14. So this is a carbon 14, Adam. And so what you'll also notice is that these three isotopes can also differ in the abundance. And so notice that this first isotope over here makes up the vast majority of all carbon atoms. In fact, it makes up about 99% of all carbon atoms, and only a small portion of all carbon atoms are made up of these other isotopes. In fact, only 1% of all carbon atoms are made up of these other two isotopes. And so the mass of these other isotopes, uh, is going to have a very small impact on the average mass of all of the isotopes. And remember, the average mass of all of the isotopes is going to be the atomic mass, which is different than the mass numbers that we just calculated here. These numbers that you see here are the mass numbers, and the atomic mass is once again going to be the average mass of all of the isotopes. So the atomic mass we're showing you over here. Considering 100% of these carbon atoms, we have to take the average. And once again, because 99% of all of the carbon atoms are carbon 12, the average is gonna be really, really close to, uh, the mass number of the most abundant isotope. And so that's why it's 12.11 The 0.11 is coming from the small, tiny percentage of isotopes that are slightly heavier than 12. And so this year concludes our introduction to isotopes. And we'll be able to get some practice as we move along through our course. So I'll see you all in our next video.

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