3 - Electron Configurations & Periodic Table Chemistry 111...

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Chemistry 111 Electron Configurations Harwood 1 Electrons are arranged in a series of energy levels which are spaced around the nucleus. These energy levels each have an “ n ” number associated with it (also known as the principle quantum number). The energy level closest to the nucleus is n = 1. Electrons in the n = 1 energy level are closest to the nucleus and have the lowest energy. Electrons in the n = 2 energy level are next closest to the nucleus and have the second lowest energy, and so on. Example : Hydrogen atom The hydrogen atom contains only one electron. When we consider atoms other than hydrogen, we have more than one electron to deal with. These electrons will repel each other (because of their negative charges); because of this repulsion between electrons the energy levels of multi- electron atoms are more complex as shown below. The s, p, d, f, etc. are labels we give to orbitals (electron clouds) of differing shapes. Figure 1 Why do the orbitals need to be different shapes? What’s wrong with just spherical orbitals like we see in the hydrogen atom? First energy level ( n = 1) Second energy level ( n = 2) Third energy level ( n = 3) 1 proton This hydrogen atom is in what we call the “ground state” (or most stable state). The one electron (black dot) is in the lowest energy level. This hydrogen atom is in what we call an “excited state” (higher energy, less stable). The one electron (black dot) is in a higher energy level ( n = 3). When this electrons “relaxes” back down to the ground state ( n =1) it will give off its excess energy in the form of radiation (light). First energy level ( n = 1) Second energy level ( n = 2) Third energy level ( n = 3)
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CHM111 Electron Configurations 2 We can think of these different shapes as points in space where the electrons are most likely found that will minimize the repulsions they feel. The orbitals have different shapes and there is a maximum
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This note was uploaded on 02/26/2012 for the course CHEM 111 taught by Professor Cao during the Fall '07 term at Purdue University-West Lafayette.

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3 - Electron Configurations & Periodic Table Chemistry 111...

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