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.

CHAPTER 6

ELECTRONIC STRUCTURE OF

ATOMS

CHAPTER 6TOPICS

• 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 = mc2, TO DESCRIBE THE ENERGY OF A PHOTON.

• THEREFORE, E = mc2 = h = hc/ ORm = 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 = -2.178 x 10-18 J(Z2/n2)

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 (ms) DEFINES HOW ELECTRONS FILL THE ORBITALS

Orbitals

Orbitals

Orbitals

QUANTUM NUMBERS

• n = PRINCIPAL ENERGY LEVELVALUES: 1, 2, 3, 4, 5, 6, 7

• l = ANGULAR MOMENTUMVALUES: 0, 1, 2, 3, ….n-1NOTE: 0 s, 1 p, 2 d, 3 f

• m = MAGNETICVALUES: + l …2, 1, 0, -1, -2, …- l

• ms = 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 2n2

• 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

EXAMPLESWRITE THE ELECTRON DIAGRAM & ELECTRON CONFIGURATION FOR AN

ATOM OFHHeLiBeNeNaAr