\nIsotopes | Matter | Physics | FuseSchool The periodic table divides the world into just over one hundred elements, sorted by their chemical properties. But did you know that each kind of atom is made up of a different combination of...\nIsotopes | Matter | Physics | FuseSchool The periodic table divides the world into just over one hundred elements, sorted by their chemical properties. But did you know that each kind of atom is made up of a different combination of just three sub-atomic particles. Everything around you made from just three ingredients! You’ve looked at atoms from a chemistry point of view, but we also cover them in physics too. In this video, we’re going to look at different forms of an atom, called isotopes. Before we start, let’s quickly recap the general structure of an atom. The nucleus is made up of neutrons and positively charged protons. The total number of these particles is called the mass number; they each have a relative mass of one. Orbiting the nucleus in specific patterns are negatively charged electrons. These are much lighter, in fact, their mass is so small we can usually ignore it. All atoms of a particular element will always have the same number of protons in the nucleus; this is called the atomic or proton number. Helium atoms always have two protons; never more, never less. Lithium has three protons, so the proton number is three. But neutrons are a little different. The number of neutrons in an atom can change. The differences in mass numbers is because this one has one more neutron in its nucleus. These different forms are called isotopes. So isotopes of an atom always have the same number of protons, but different numbers of neutrons. The different isotopes do however have identical chemical properties. The mass shown in the periodic table is a weighted average of all the atoms of that element. So of all the different isotopes. If it’s close to a whole number, that usually means there’s only one common isotope. For example, around 99% of carbon atoms have six neutrons. Which means about 99% of them have a mass number of 12. But around 1% have an extra neutron. We call this isotope Carbon-13. And there is Carbon-14 which is even rarer, with eight neutrons. Because most of the carbon isotopes have a mass of 12, but some have 13 and even fewer have 14, this is why the mass number on the periodic table is just a little higher than 12. Only very precise measurements can show this. Some combinations of protons and neutrons are stable. But some are unstable, which means the nucleus doesn’t last very long. These are often called radioisotopes because when they break down they give out nuclear radiation, which we’ll look at in the next video. For now, you should be happy explaining what isotopes are and linking the numbers in the periodic table to the sub-atomic particles in each atom. CREDITS Animation & Design: Waldi Apollis Narration: Dale Bennett Script: Ian Horsewell\n
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