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Electron Configuration Topic #8 September 2012 How was the Atomic Model developed? The first modern atomic theory, proposed by Dalton, portrayed the atom as a solid indivisible mass. After the discovery of the electron by J. J. Thomson, the atomic model was revised to include them. J. J. Thomson’s model is referred to as the “plum-pudding” model. Rutherford pictured the atom as a dense nucleus surrounded by electrons. In the Bohr model, the electrons move in circular paths. The quantum mechanical model is the modern description of the electrons in atoms. This model estimates the probability of finding an electron within a certain volume of space surrounding the nucleus. Schrodinger What are Atomic Orbitals? Atomic orbitals are regions around the nucleus within which the electrons have the highest probability of being found. Energy levels are regions in space around the nucleus where an electron is likely to be moving. Before we start………. Take out your Periodic Table ONLY one paper and pencil/pen for you and your shoulder partner Using Rally Robin……. Discuss what Mr. Tapia is doing on the board!! Try to relate what he is writing on the board and the handout you received when you entered the room 1st partner has 30 seconds to tell the other partner his/her ideas 2nd partner has now 30 seconds to share his/her ideas with the 1st partner General Patterns of Filling Orbitals Let’s Practice Using Rally Coach! Write the electron configuration for the following atoms: 1.C 2. S 3. K 4. Ar 1s2 2s2 2p2 1s2 2s2 2p6 3s2 3p4 1s2 2s2 2p6 3s2 3p6 4s1 1s2 2s2 2p6 3s2 3p6 Let’s Practice Using Rally Coach! Write the electron configuration for the following atoms: Rubidium Helium Phosphorus Iron Arsenic 1s22s22p63s23p64s23d104p65s1 1s2 1s22s22p63s23p3 1s22s22p63s23p64s23d6 1s22s22p63s23p64s23d104p3 Let’s Practice! Which atoms are these? 1. 1s2 2s2 2p4 2. 1s2 2s2 2p6 3s2 3p2 3. 1s2 2s2 2p6 3s2 3p6 4s2 4. 1s2 2s2 2p6 3s2 3p5 1.O 2.Si 3.Ca 4.Cl THE ELECTRON CONFIGURATION E.Q.: HOW IS THE ARRANGEMENT OF ELECTRONS EXPRESSED THROUGH ELECTRON CONFIGURATIONS AND LEWIS DOT STRUCTURES? How are Electrons Arranged in an Atom? The ways in which electrons are arranged around the nuclei of atoms are called electron configurations. It is also the most stable arrangement of electrons around the nucleus of an atom (ground state of electrons). Noble Gas Notation for Electron Configuration You do not have to repeat yourself over and over 1. Oxygen 1s22s22p4 [He] 2s2 2p4 2. Silicon 1s22s22p63s23p2 [Ne] 3s2 3p2 3. Calcium 1s22s22p63s23p64s2 [Ar] 4s2 22s22p63s23p5 1s 4. Chlorine [Ne] 3s2 3p5 How are Electron Configurations for Atoms written? Rules that govern Electron Configuration: 1. Aufbau principle Electrons enter orbitals of lowest energy first. 2. Hund’s rule When electrons occupy orbitals of equal energy, one electron enters each orbital until all the orbitals contain one electron with parallel spin. 3. Pauli exclusion principle An atomic orbital may describe at most two electrons with opposite spins. General Patterns of Filling Orbitals Bell Ringer Give both the expanded and noble gas notation for the elements… 1. 2. 3. 4. 5. [He] 2s22p3 Nitrogen 1s22s22p3 Argon 1s22s22p63s23p6 [Ne] 3s23p6 Titanium 1s22s22p63s23p64s23d2 [Ar] 4s23d2 Selenium1s22s22p63s23p64s23d104p4 [Ar]4s23d104p Strontium 1s22s22p63s23p64s23d104p65s2 [Kr]5s2 References Wilbraham, Antony C., Dennis C. Staley, Michael S. Matta, and Edward L. Waterman. Chemistry. New Jersey: Prentice Hall, 2002. Summary of Principal Energy Levels, Sublevels, and Orbitals Principal Energy Level Number of Sublevels Type of Sublevel n=1 1 1s (1 orbital) n=2 2 2s (1 orbital) 2p (3 orbitals) n=3 3 3s (1 orbital) 3p (3 orbitals) 3d (5 orbitals) n=4 4 4s (1 orbital) 4p (3 orbitals) 4d (5 orbitals) 4f (7 orbitals)