Isotopes are elements with the same number of protons, but a different number of neutrons. Now, with this whole idea of isotopes, we're going to be introduced to some new terms. The first term is atomic number. Atomic number uses the variable Z. It provides the number of protons. So basically, if I have an unknown element, but I know its atomic number, I can go to the periodic table, look up that atomic number, and it'll give me the identity of that unknown element. And because of this, we're going to say it helps us determine the identity and chemical properties of an element. The whole aspect of chemical properties of an element, we'll discuss much later on in later chapters.
Now, besides atomic number, we have mass number, which uses the variable A. This one provides the number of protons and neutrons. Now we're going to say to calculate the number of neutrons, we can just take the mass number A and subtract the atomic number Z. That'll tell us the number of neutrons for any given isotope or element.
Now if we take an atomic view of an atom, remember, an atom is composed of 4 primary parts. We have our nucleus, which houses the neutrons and protons, and we have our electrons, which spin around the nucleus. Now if we take a look here at this example, we know that our neutrons, colored as red, if we take a look at this atom, we have 1, 2, 3, 4, 5, and 6 for this particular atom. Protons, which we show as blue, we have in this example, 1, 2, 3, 4, 5 protons. The electrons are the green spheres that are rotating or orbiting the nucleus. We have 1, 2, 3, 4, 5 electrons. Now remember mass number we said is the number of protons, which is 5, plus the number of neutrons, which in this example is 6. When you add those together that gives us the mass number, which comes out to be 11. So just remember, blue and red mixed together give us the color purple. So we're using this purple A to designate our mass number for this particular atom.
Now, we said earlier that the atomic number gives us the number of protons. So if you know the number of protons, you know your atomic number. In this example, because we have 5 protons, our atomic number has to be 5, and because we know the atomic number is 5, we know the element identity. Here, we don't show an example of a periodic table. We'll go into greater discussion on it later on. But if we were to look at a periodic table, look for the atomic number 5, we'd see that it belongs to the element of boron. So this atom is an illustration of the element boron. And speaking of this atom, we're going to say for a neutral element, which is oftentimes called an atom, the number of protons and electrons are equal. And this makes sense because, remember, protons are positively charged, and electrons are negatively charged. If you have equal numbers of positive and negative charges, they're going to cancel one another out, and you'll be left with a neutral element. So just remember, when we're dealing with a neutral element, that's another way of saying atom. In an atom, the number of protons and electrons are equal. Now later on, we'll talk about other species called ions. In ions, the number of protons and electrons are not equal. But for right now, just realize that when they're throwing in the words neutral element or atom, we're dealing with a species or an element that has the same number of protons and electrons. Now that we've looked at the atomic view of the atom, now that we've incorporated these new terms of mass number and atomic number, let's continue our discussion and exploration of the atom itself.