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Metallic Character and the Periodic Table
I want you to think about metals. What comes to mind? My first thought was a nice shiny penny. It's kind of silly. But, there's something surprisingly satisfying about the luster of a new penny. But, what makes something a metal? At first, we might think of their physical properties. They're shiny, malleable, and conductive. But, I can think of some nonmetal compounds that are shiny. For example, diamond sparkles way more than any metal. Even glass can appear shinier than some metals. Let's think about the chemical properties we've been studying.
We just studied ionization energy. So, we know atoms can lose electrons. The smaller their atomic radius, the more tightly they hold them. So, it requires more energy to pull them away. But, did you know it also determines the type of element? Metals, metalloids, and nonmetals all do different things with their electrons. Today we'll study the characteristics of metals!
Consider the alkali metals. They're the periodic table's stereotypical metals. They have one valence electron, and it's easy to remove. What trend are we seeing? Metallic character depends on how easily the valence electrons are extracted. Electrons are more easily removed when their attraction to the nucleus decreases. So, atomic orbitals, the electron configuration, and the atom radius all play a role in metallic character.
Across the periodic table, left to right, the metallic character decreases. As you move to the right, the atoms are more likely to accept electrons than lose them. Why? They have larger electronegativities. They want electrons to complete their octet. Think about the halogens. It's so easy for them to gain an electron. They're so close to the noble gas ion configuration! They are the stereotypical nonmetal. We also know that the atomic radius is decreasing. As we increase the atomic number, there are more protons. But, the number of core electrons remains constant. So, the valence electrons experience less shielding. The nucleus' attraction is more robust.
What about moving down the periodic table? Metallic character increases! As you move down a group, the atom becomes more extensive. There are more electrons. More electrons equal more filled orbitals. So, more core electrons shield the valence electrons from the nucleus. But, it also means the valence shell is further from the atom's nucleus. So, it's easier to remove.
The Most and Least Metallic Elements
So, what element is the most metallic? Honestly, it's a little bit of a trick question. Based on the periodic table, it's francium. But, it is a radioactive element. Francium has an unstable nucleus. So, it decays very quickly. Nuclear decay rates are measured in half-lives. The most prolonged half-life of any francium isotope is 22 minutes! Where do we even get francium? It's formed by Uranium's decay chain. Environmental chemists estimate only about 30.0 grams of francium are in the earth's crust. That's not very much! Of the naturally occurring elements, cesium is the most metallic. But, even cesium isn't very abundant.
What element has the least metallic character? Helium! It's in the upper right of the periodic table. So, we would expect it to have basically zero metallic characteristics. But did you know metallic helium exists? At massive temperatures and pressures, the nuclei form into a crystal lattice. What about the electrons? They become delocalized. So, we basically have metallic bonding! But, what magnitude of temperatures and pressures do we need? About 10,000 to 20,000 kelvin and 70 million atmospheres. Where in the world is that even possible? It's not conceivable on earth. It happens at the centers of massive planets like Jupiter and Saturn.
