Periodic Properties

Periodic Properties - Many Electron Atoms and Periodic...

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1 Many Electron Atoms and Periodic Properties . I. Electron Structure A. The Aufbau Principle. 1. We can solve Schrödinger equation only for the hydrogen atom. Therefore, we will build up the structure of many electron atoms in the following way: a. Start with hydrogen solutions. Increase the nuclear charge by one and place another electron in atom. Starting with the hydrogen solutions, use the rules of quantum mechanics to determine the energy and wave function of the two electron system; this is the structure of He. b. To obtain structure of Li, start with the He results, increase nuclear charge by one and add another electron. This process is repeated and the structures of the heavier atoms are obtained by " building out " from lighter atoms. (Aufbau = building out) 2. The results. a. n, l,m l and m s are still good quantum numbers for describing the behavior of the electrons, that is, the electrons exist in hydrogen-like orbitals. b. In the absence of strong magnetic fields, the energy depends on both n and l . The order of the subshells encountered in following the aufbau principle is: 1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s .... c. This sequence can be remembered by the following scheme: 1s 2s 2p 3s 3p 3d Follow the diagonals. 4s 4p 4d 4f 5s 5p 5d 5f 5g 6s 6p 6d 6f 6g 6h 7s 7p 7d 7f 7g 7h 7I 8s 8p 8d…….. 3. The electron structure of an atom is given by writing the electron configuration of the atom. a. Examples element: 1 H 2 He 3 Li 5 B 6 C 7 N electron configuration: 1s 1 1s 2 1s 2 2s 1 1s 2 2s 2 2p 1 1s 2 2s 2 2p 2 1s 2 2s 2 2p 3 32 Ge: 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 2 or : 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 2 Could also group according to n, but fill according to the aufbau principle Write the subshells occupied and the number of electrons in the particular subshell as a right-hand superscript.
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2 b. The most important electrons in determining the physical and chemical properties of an element are the outermost or valence electrons . 1) For the main group elements the valence electrons are all those electrons with the highest value of the principle quantum number n, they will be s and p electrons. 2) The inner electrons are called the core electrons . They are chemically inert. Their main function is to shield the nuclear charge as seen by the valence electrons. 3) Example: electron division in Ge: 32 Ge: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 2 core valence 4) Some valence configuration are: 3 Li 2s 1 5 B 2s 2 2p 1 6 C 2s 2 2p 2 7 N 2s 2 2p 3 B. Periodic Table and Valence Electron Configuration. 1. Main group elements (Representative elements, s and p-block elements) a. Valence electrons are s and p electrons b. All elements in the same group have the same valence electron configuration. 1) Group 1 (alkali metals) H Li Na K Rb Cs Fr 1s 1 2s 1 3s 1 4s 1 5s 1 6s 1 7s 1 All group 1 elements have an s 1 valence configuration 2) Group 17 (halogens) F Cl Br I At 2s 2 2p 5 3s 2 3p 5 4s 2 4p 5 5s 2 5p 5 6s 2 6p 5 All group 17 elements have an s 2 p 5 valence electron configuration c. For the main group elements
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