 In this video, we're going to discuss the periodic properties related to valence electrons, metallic character, and ionization energy. The first thing we're going to discuss is valence electrons. Valence electrons are the electrons on the highest energy level of an atom. So if we look at the periodic table, first thing we can tell is, the first thing to notice is the group numbers. Group numbers are designated either with just numbers as in 1 through 18, or we have a lettering system as well. So we have the 1A, 2A, 3A through 8A, and then in the middle here we have our B elements which are transition metals. I tend to use the AB lettering system because it differentiates between the representative elements that tend to follow the rules and the transition metals are elements that tend not to follow the rules. So for our representative elements, the A groups, whatever the group number is, that's how many valence electrons are in that specific atom. So carbon, for example, is in group 4A. Carbon's in group 4A, has four valence electrons. In group 2A, it will have two valence electrons. Now that does not work for the B elements. You can't tell how many valence electrons a group B element has just by its group number. So if we look at nickel, for example, its group number is 8B. It does not have eight valence electrons, but I'm going to show you how you can use electron configurations to determine the number of valence electrons. So for nickel, it ends in 3D8. So we're going to write the electron configuration for that element, 1S2, 2S2, 2P6, 3S2, 3P6, 4S2, 3D8. So that would be the electron configuration for nickel. We need to find the highest energy level. The energy levels are designated by the numbers. So 4 would be the highest energy level. On the fourth energy level, we have two electrons. So that means that nickel has two valence electrons. Using electron configurations will work for the representative elements as well if you want to choose an element from the periodic table like oxygen. Oxygen has eight total electrons. Based on its group number, we would expect it to have six valence electrons. When we do the electron configuration for oxygen, we have a total of eight electrons total. The highest energy level is two. On the second energy level, we have electrons in the S sub-level and the P. So we would have to add them up. So that means we have a total of six valence electrons for oxygen, which matches the group number. So you can use the electron configuration for either group A or group B elements. For group A elements, you can refer to the periodic table and just look at the group number. So the valence electrons are the electrons on the highest energy level. They're going to be the ones that are associated with bonding and the reactivity of the atom. And so those are the ones that we need to focus on when we start looking into bonding. Other properties, periodic properties that we can look at, metallic character is one of them. Basically, metals tend to be shiny, good conductors of heat and electricity. They tend to be ductile and malleable elements. So the more metallic characteristics an atom has, the more metal-like it is. Metallic character increases going down a group. So as you go down the group, we have the least metallic character at the top and it increases going down. In terms of metallic character, it's going to decrease as we go across the periodic table. As you recall, nonmetals are on the right side of the periodic table. Your metals are on the left side of the periodic table. So as we go across from left to right, we start with metals and then they change into metalloids into nonmetals. So the metallic character is going to decrease as you go across the periodic table from left to right. Another periodic trend that we can look at is size, radius of the atoms. In terms of size, this chart, this periodic table shows you the atomic radius of the elements. As we go down a group or a vertical column, the size gets larger. We start with level one. We only have one level of electrons. On level two, we have two, three, four, five. They get larger and larger. Going across from left to right, however, you'll notice that they start out large and they start getting smaller and smaller. Even though the atomic number is increasing, which means more protons in the nucleus and more electrons outside the nucleus, there's actually a greater attraction between the electrons outside the nucleus and the protons in the nucleus and the atom tends to compress a little bit and it gets a little bit smaller. So if we look at elements, sodium, for example, has an atomic radius of 166 picometers. And if we go to the other end of the period, we have argon, which has an atomic radius of 106 picometers. So there's a decrease there from 166 to 106 picometers. So that trend is the same across each row of the periodic table. So we can use the periodic table to identify the number of valence electrons. We can also use it to compare the metallic character and the atomic radius of atoms on the periodic table.