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Its professor David let's talk about the periodic table pretty much everyone knows with this is even if they don't know much about chemistry. It's the periodic table of the elements which at first seems like a random arrangement of substances most of which sounds strange and foreign but the way the elements are arranged reveals many beautiful patterns that tell us about how nature operates. In the mid 1800s lots of chemists were trying to come up with a way to depict all the elements in table form and many formats were proposed, but it was the one by Dmitri Mendeleev that stuck because of how well it correlates data as well as its predictive powers. He arranged the elements into rows called periods and columns called groups elements that had similar behavior were put in groups together which helped to correlate existing data, and it also predicted the existence of elements that had never been seen before. With the gaps in the table Mendeleev said there must be elements that go in these spots, and he predicted some of their properties eventually these elements were discovered with the properties precisely as expected, and now we have all the metals, metalloids and nonmetals organized nicely it wasn't known at the time, but the reason elements in the same group behave similarly is because they have the same number of valence electrons. Look at group one for example, these elements all have one valence electron or one electron in their outermost shell. As you go down the table and n increases you gain a shell each time, but whichever is the outermost shell there is only one electron in it. Every element in group 2 has two electrons in its outermost shell and so forth this simple fact determines many characteristics about each element in ways we will continue to see as we learn more chemistry. There are some periodic trends that we can recognize when we look at the table. The first one is an atomic radius or the size of the atom. As we proceed downward on the table atomic size increases because we add shells. As we go to the right atomic radius decreases because we are moving within a shell and each element to the right has one more proton in the nucleus than the last, so there is a stronger electromagnetic attraction felt by the electrons and the radius shrinks, that means overall atomic radius increases going this way on the periodic table ionic radius is a little different, electrons repel each other so adding an electron makes an atom bigger. Taking one away makes it smaller ions with the same electron configuration will have their radii decrease as the atomic number increases next we look at ionization energy. This is the energy required to remove an electron from the atom. It will always be an electron in the outermost shell. The electromagnetic force that attracts the electrons to the protons drops off very quickly with distance so the farther away an electron is from the nucleus the easier it is to pull it away. This means the ionization...