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.

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.

General Patterns of Filling Orbitals

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.

General Patterns of Filling Orbitals

Let’s Practice! Write the electron configuration for the following atoms: 1.C 2.S 3.K 4.Ar 1s 2 2s 2 2p 2 1s 2 2s 2 2p 6 3s 2 3p 4 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 1s 2 2s 2 2p 6 3s 2 3p 6

Let’s Practice! Which atoms are these? 1. 1s 2 2s 2 2p 4 1.O 2.Si 3.Ca 4.Cl 2. 1s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p 5

Noble Gas Notation for Electron Configuration You do not have to repeat yourself over and over 1.Oxygen  1s 2 2s 2 2p 4 [He] 2s 2 2p 4 2. Silicon  1s 2 2s 2 2p 6 3s 2 3p 2 [Ne] 3s 2 3p 2 3. Calcium  1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 [Ar] 4s 2 4. Chlorine  1s 2 2s 2 2p 6 3s 2 3p 5 [Ne] 3s 2 3p 5

Your turn. Give both the expanded electron notation and the noble gas notation on blank page of notes. Nitrogen Argon Titanium Selenium Strontium Fluorine

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 = 111s (1 orbital) n = 222s (1 orbital) 2p (3 orbitals) n = 333s (1 orbital) 3p (3 orbitals) 3d (5 orbitals) n = 444s (1 orbital) 4p (3 orbitals) 4d (5 orbitals) 4f (7 orbitals)