Hello again. I'm going to start off today's post with a little fun. What do you get when you take the works of an EXTREMELY enthusiastic physicist and writer, and turn it into an awesome song? You get a kick ass science themed music. The late Carl Sagan was a scientist and writer who never lost his awe and love of science, and one guy with a keyboard and an auto tune program made this tribute.
Now on to the chemistry. Last week my class looked at trends in the periodic table, and how it relates to effective nuclear charge. For any of the uninitiated, that is the pull any one electron feels from the nucleus. This is based off of all the electrons between that electron and the nucleus, which serve to dampen the pull, like coats blocking out the cold. This is a pretty big deal, because this affects the valence electrons, being the electrons that react with other atoms, (molecules are from two or more elements sharing electrons). My group has to do a presentation of ionization energy, which is the energy required to take an electron away from an element. This is pretty related to that effective nuclear charge thingy, basically because the more pull the nucleus has on that one valence electron we are talking about at the time.
WOOO! Lets slow that down a bit. Heres a metaphor to bring it down to simpler terms.
So lets say that every atom is like a magnet and a box of paperclips. Remember that? You take a magnet, and you dangle a huge chain of paperclips from that magnet, all of them connected by a stream of magnetism. Now take that imaginary chain and pick a paper clip. Grab it there and try to rip it off of the chain. Now grab a paper clip closer to the magnet, say, the one right next to it. It should take more energy to rip it off because the pull of the magnet is stronger the closer the paper clip is to the magnet. The paper clip farther out has less of a pull because the magnetic charge is kind of diluted by the other paper clips between that one clip and the magnet. Electrons and the nucleus are like the paper clips and the magnet. So if we go up to Fluorine, which has its last last bunch of electrons attached to a chain of only two electrons, with a magnet with nine protons. So if you wanted to rip off that electron, that paperclip, you have to fight the pull of that VERY close magnet. Takes a lot of energy to pull this off. Now take Francium. It has a valence electron way the hell out there, on a long chain of 86 electrons to a magnet of 87 electrons. That electron is practically dropping off the chain. THAT is how ionization energy works. Fluorine has a larger ionization energy than francium because its valence electrons have a larger effective nuclear charge. TADA! Difficult explanation finished. Effective Nuclear Charge is like gravity. It effects everything else in the chapter and much more. Such as:
Electron Affinity: The evil twin to ionization energy. How easily a sneaky element steals other electrons. Based off of the effective nuclear charge by how much pull the nucleus has on another electron TO STEAL THE SHINY GOLD ELECTRON MWAH HA HA. Measured in energy released when the electron is added to the element. If the value is positive, then that means that energy must be input into the atom for it to accept that electron. If it is negative, then that electron will cause energy to be released. Elements with a high effective nuclear charge have a high electron affinity, but the larger the element, the more electron affinity it has. This is because larger atoms are less dense, and its easier for the electron to fit into an orbital.
Atomic Radius: Bit tricky. Atomic radius is the distance from the nucleus that the element will bond with other elements. I use the metaphor of legos. Say that those paper clips are separated into levels, and each level fills up one at a time as long as the element is at a ground state (means it isnt being excited by lots of heat or something) and other elements can ONLY bond to the most outer most level, kind of like a tower of legos. You can only connect them at the very outer part where all the bumps are. So the more levels there are, the farther out the element will bond with others. Effective Nuclear Charge is the number of protons minus the number of electrons in the levels below it, or the levels of the legos. So since the levels of legos increase the radius, that means the more electrons there are the larger the radius. Now also, there is only a new lego level on each row of the periodic table, so if you travel left on the periodic table, you should get a larger radius. Also, the less effective nuclear charge, the less pull the magnet has on all the levels, and it spreads out a bit more. If the effective nuclear charge was stronger, the levels would be more compact and thus smaller. Down and left, the radius increases. Now the thing about effective nuclear charge is that it increases in the exact opposite directions. ITS ALL RELATED.
This is a long post, so I will leave it there. I will post again tomorrow, maybe about metal and nonmetal oxides, and I will see you again next time. First, I will leave you with this other Sagan related video. Matrix style baby. Hopefully you don't feel like Morpheus there after reading the post.
