CHAPTER 6 ELECTRONIC STRUCTURE OF ATOMS

CHAPTER 6 TOPICS THE QUANTUM MECHANICAL MODEL OF THE ATOM USE THE MODEL IN CHAPTER 7 TO EXPLAIN THE PERIODIC TABLE AND THE TRENDS OF THE ELEMENTS IN THE TABLE USE THE MODEL IN CHAPTERS 8 & 9 TO EXPLAIN CHEMICAL BONDING AND THE STRUCTURE AND SHAPE OF MOLECULES

HISTORY THE QUANTUM MECHANICAL MODEL OF THE ATOM IS BASED ON: THE NATURE OF LIGHT AND MATTER & A NEW FIELD OF MATHEMATICS

HISTORY MATTER IS ANYTHING THAT HAS MASS AND OCCUPIES SPACE

HISTORY LIGHT (ALSO KNOWN AS ELECTROMAGNETIC RADIATION) IS A FORM OF ENERGY (VISIBLE LIGHT IS ONLY ONE FORM OF ELECTROMAGNETIC RADIATION)

HISTORY ELECTROMAGNETIC RADIATION CAN BE DESCRIBED AS A SINE WAVE, THEREFORE:   = c WHERE:  = WAVELENGTH  = FREQUENCY c = SPEED OF LIGHT  E = h  = hc/ WHERE  E = ENERGY h = PLANCK’S CONSTANT

The Electromagnetic Spectrum

HISTORY LIGHT TRAVELS IN DISCRETE PACKAGES OF SPECIFIC ENERGY. THESE PACKAGES ARE CALLED PHOTONS. EINSTEIN PROPOSED, E = mc 2, TO DESCRIBE THE ENERGY OF A PHOTON. THEREFORE, E = mc 2 = h  = hc/ OR m = h/(c  THUS LIGHT HAS MASS!

HISTORY SUMMARY ELECTROMAGNETIC RADIATION IS QUANTIZED (LIGHT TRAVELS IN PACKETS OF SPECIFIC ENERGY CALLED PHOTONS (QUANTA) ELECTROMAGNETIC RADIATION HAS THE PROPERTIES OF BOTH ENERGY AND MATTER MATTER HAS THE PROPERTIES OF ELECTROMAGNETIC RADIATION

HISTORY BOHR MODEL OF THE ATOM WAS BASED ON CLASSICAL PHYSICS E = x J(Z 2 /n 2 ) WHERE:Z = NUCLEAR CHARGE n = INTEGER (ORBIT) MODEL WORKS PERFECT FOR H ATOM, WINS NOBEL PRIZE FOR BOHR MODEL FAILS FOR ALL OTHER ATOMS

HISTORY IN 1925, A MATHEMATICIAN, ERWIN SCHROEDINGER PROPOSED A NEW MODEL FOR THE HYDROGEN ATOM

HISTORY SCHROEDINGER’S MODEL WAS BASED ON: –DESCRIBING THE ATOM BY CONSIDERING THE e - ONLY –DESCRIBING THE e - AS BOTH A PARTICLE AND AS ENERGY –THE e - WAS DESCRIBED BY A SINE WAVE,  –ENERGY OF e - WAS QUANTIZED

Solution To Schroedinger Equation SET OF EQUATIONS,  1,  2,  3, …….. EACH EQUATION DESCRIBES AN ORBITAL IN WHICH THE ELECTRONS MAY BE LOCATED THE ORBITALS ARE DESCRIBED BY 4 QUANTUM NUMBERS e - HAVE THE SAME QUANTUM NUMBERS AS THE ORBITAL IN WHICH THEY RESIDE

QUANTUM NUMBERS FIRST 3 QUANTUM NUMBERS DEFINE THE ORBITALS AND THEIR ENERGY  n – SIZE OF ORBITAL  l – SHAPE OF ORBITAL  m – ORIENTATION & NUMBER OF ORBITALS FOURTH QUANTUM NUMBER (m s ) DEFINES HOW ELECTRONS FILL THE ORBITALS

Orbitals

QUANTUM NUMBERS n = PRINCIPAL ENERGY LEVEL  VALUES: 1, 2, 3, 4, 5, 6, 7 l = ANGULAR MOMENTUM  VALUES: 0, 1, 2, 3, ….n-1  NOTE: 0  s, 1  p, 2  d, 3  f m = MAGNETIC  VALUES: + l …2, 1, 0, -1, -2, …- l m s = SPIN  VALUES: +1/2 OR –1/2

QUANTUM NUMBERS ORBITALS OF THE SAME ENERGY, ( i.e. SAME n AND l QUANTUM NUMBERS) ARE CALLED DEGENERATE ORDER OF INCREASING ENERGY OF THE ORBITALS IS: 1s, 2s, 2p, 3s, 3p, 4s*, 3d, 4p, 5s*, ……. * RATIONALE FOR THESE DEVIATIONS WILL BE SEEN LATER

FILLING ORBITALS WITH ELECTRONS MAX # OF e - IN A PRINCIPAL ENERGY LEVEL IS 2n 2 NO MORE THAN 2 e - PER ORBITAL (PAULI EXCLUSON PRINCIPLE) FILL LOWEST ORBITALS FIRST FILL ORBITALS OF SAME ENERGY WITH ONE e - EACH. WHEN ALL HAVE ONE e -, ADD THE SECOND e -

GOLDEN RULE IN AN ATOM, NO TWO ELECTRONS CAN HAVE THE SAME FOUR QUANTUM NUMBERS

MODELS OF THE ATOM 1. ELECTRON DIAGRAM 2. ELECTRON CONFIGURATION

Electron Energy Levels

Electron Diagram

Electron Diagrams and Electron Configurations

EXAMPLES WRITE THE ELECTRON DIAGRAM & ELECTRON CONFIGURATION FOR AN ATOM OF H He Li Be Ne Na Ar