ELECTRON CONFIGURATION Section 5.2

Stability  Lowest possible energy

Energy levels  The maximum number of electrons in the principle energy level (shell) is 2n 2. Energy Level (n)Maximum # of e

Electron Configuration  The Electron Configuration tells us how many electrons exist in each principal energy level (n=1-7) Atomic Number-6 Mass Number- 12  6 protons  6 neutrons  6 electrons  Electron Configuration- 2-4

Electron Configuration  The electron configuration for the ground state of an atom is given on the Periodic Table of the Elements K Electron Configuration

What is the electron configuration of a sulfur atom in the ground state? (1) 2-4 (2) 2-6 (3) (4) 2-8-6

Three Rules  Aufbau principle  Pauli exclusion principle  Hund’s rule

Aufbau Principle  Electrons occupy the orbital of lowest energy first.

Orbitals  spdf- comes from a now-discredited system of categorizing spectral lines  s- “strong”  p- “principal”  d- “diffuse”  f- “fundamental”

s orbital  spherical

p orbitals  Dumb bell shaped

d orbitals  Double dumb bell shaped

f orbitals  Very complicated  Rare earth elements

Energy levels  sublevels  orbitals Principal Energy Level Number of sublevels Type of sublevel n=111s (1 orbital) n=222s (1), 2p (3) n=333s (1), 3p (3), 3d (5) n=444s(1), 4p (3), 4d (5), 4f (7)

Orbitals- Number of electrons  s-1 orbital= 2 e -  p-3 orbitals= 6 e -  d-5 orbitals= 10 e -  f-7 orbitals= 14 e -

Filling Orbitals 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f (5g) 6s 6p 6d (6f 6g 6h) 7s 7p (7d 7f 7g 7h 7i)

Pauli Exclusion Principle  An atomic orbital may describe at most 2 electrons.  Those two electrons must have opposite spins  Spin: a quantum mechanical property of electrons (clockwise/counterclockwise) 

Hund’s Rule  Electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible.    

Exceptions  Some actual electron configurations differ from those assigned using the Aufbau principle  This leads to variation in chemical behavior

Valence Electrons  Outermost electrons  Participate in reactions Properties of elements  Coincides with groups on the Periodic Table

Kernel  The nucleus and inner electrons 2 valence e - KERNEL

 What is the total number of valence electrons in an atom of electron configuration X?  Which electron configuration represents the excited state of a calcium atom? ElementElectron Configuration X Y Z

What is the total number of electrons in the valence shell of an atom of aluminum in the ground state? (1)8 (2)2 (3)3 (4)10

Lewis Dot Structures  Diagrams that show valence electrons as dots

Lewis (Electron) Dot Structures C

Your Turn  Draw the Lewis Dot Structures for the following elements: Hg, Mn, K, Au, Cs