ELECTRONIC STRUCTURES

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ELECTRONIC STRUCTURES This page explores how you write electronic structures for atoms using s, p, and d notation. It assumes that you know about simple atomic orbitals - at least as far as the way they are named, and their relative energies. If you want to look at the electronic structures of simple monatomic ions (such as Cl - , Ca 2+ and Cr 3+ ), you will find a link at the bottom of the page. http://www.chemguide.co.uk/atoms/properties/elstructs.html#top
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The electronic structures of atoms Relating orbital filling to the Periodic Table This page looks in detail at the elements in the shortened version of the Periodic Table above, and then shows how you could work out the structures of some bigger atoms.
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The first period Hydrogen has its only electron in the 1s orbital - 1s 1 , and at helium the first level is completely full - 1s 2 .
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The second period Now we need to start filling the second level, and hence start the second period. Lithium's electron goes into the 2s orbital because that has a lower energy than the 2p orbitals. Lithium has an electronic structure of 1s 2 2s 1 . Beryllium adds a second electron to this same level - 1s 2 2s 2 . Now the 2p levels start to fill. These levels all have the same energy, and so the electrons go in singly at first.
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The second period B 1s 2 2s 2 2p x 1 C 1s 2 2s 2 2p x 1 2p y 1 N 1s 2 2s 2 2p x 1 2p y 1 2p z 1
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The second period The next electrons to go in will have to pair up with those already there. O 1s 2 2s 2 2p x 2 2p y 1 2p z 1 F 1s 2 2s 2 2p x 2 2p y 2 2p z 1 Ne 1s 2 2s 2 2p x 2 2p y 2 2p z 2 You can see that it is going to get progressively tedious to write the full electronic structures of atoms as the number of electrons increases. There are two ways around this, and you must be familiar with both.
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Shortcut 1: All the various p electrons can be lumped together. For example, fluorine could be written as 1s 2 2s 2 2p 5 , and neon as 1s 2 2s 2 2p 6 . This is what is normally done if the electrons are in an inner layer. If the electrons are in the bonding level (those on the outside of the atom), they are sometimes written in shorthand, sometimes in full. Don't worry about this. Be prepared to meet either version, but if you are asked for the electronic structure of something in an exam, write it out in full showing all the p x , p y and p z orbitals in the outer level separately.
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For example, although we haven't yet met the electronic structure of chlorine, you could write it as 1s 2 2s 2 2p 6 3s 2 3p x 2 3p y 2 3p z 1 . Notice that the 2p electrons are all lumped
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This note was uploaded on 12/28/2011 for the course CHEM 2045 taught by Professor Gower during the Fall '11 term at University of Florida.

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ELECTRONIC STRUCTURES - ELECTRONIC STRUCTURES This page...

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