And that's why you could use the atomic number to identify our x, our element. The second that the number of protons changes that means our element also changes. Now let's go into something called isotopes of elements. Now, two or more atoms that contain the same number of protons mean they're the same elements but have different number of neutrons, are called isotopes of that same. Let's look at a very common example of carbon. Now carbon has three isotopes.