Modern Atomic Theory- Electronic Structure of Atoms · 2010. 11. 22. · Modern Atomic...

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Modern Atomic Theory- Electronic Structure of Atoms DR HNIMIR-CH7 Problems with the atomic model? Where should (-) electrons be found?

Transcript of Modern Atomic Theory- Electronic Structure of Atoms · 2010. 11. 22. · Modern Atomic...

Page 1: Modern Atomic Theory- Electronic Structure of Atoms · 2010. 11. 22. · Modern Atomic Theory-Electronic Structure of Atoms DR HNIMIR-CH7 Problems with the atomic model? Where should

Modern Atomic Theory-Electronic Structure of Atoms

DR HNIMIR-CH7

Problems with the atomic model?Where should (-) electrons be found?

Page 2: Modern Atomic Theory- Electronic Structure of Atoms · 2010. 11. 22. · Modern Atomic Theory-Electronic Structure of Atoms DR HNIMIR-CH7 Problems with the atomic model? Where should

First, a Little About Electromagnetic Radiation- Waves

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Another Look

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Relationship

λλλλ νννν = c

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Planck’s Relationshipblack body radiation experiment

∆E = h ν

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ProblemFor green visible light of wavelength 486 nm

a. what is the frequency of this radiation?

b. Calculate ∆E

λλλλ νννν = c

∆E = h ν

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Meaning of results?

4.086x10-19 J is the minmum amount of energy to be gotten from this green light. If you want more,

you have to take 2 x 4.086x10-19 J (or 3x, 4x, etc)

4.086x10-19 J

green light of wavelength 486.0 nm comes "packaged" in packets

(called quanta in general and photons for EM) of 4.086x10-19 J

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Two More ThingsFor red light of wavelength 725.0 nm

∆E is 2.740x10-19J

2.740x10-19J

When you calculate ∆E the units are actually J/photon

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The EM Spectrum

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Einstein’s Involvement

"particle / wave dualism"

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The Photoelectric Effect

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Frauhoffer LinesWith good optics it was noticed that

the continuous spectrum obtained from the sunhad very fine black lines in it

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Line SpectraThe Bohr Atom

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The Hydrogen Spectrum

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The Bohr ModelNiels Bohr interprets the lines as quantized energy emitted by electrons between allowed energy levels

1

2

3

4

an electron absorbs energy and is promoted to

a higher energy level

1

2

3

4

the excited electron returns to a lower energy level and emits a specific amount of energyseen as a sharp line of light

1

2

3

4

∆E

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Bohr Orbits

Bohr calculates the energy of the nth orbit by the formula

En = -B

n2

where B= 2.180x10-18J for the hydrogen atom

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ProblemCalculate the energy of the 2nd and 4th energy levels

En = -2.180x10-18J

n2

Calculate ∆∆∆∆E for the transition (∆∆∆∆E= E2-E4)

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Calculate the Wavelength (in nm) Associated with the Answer from

the Last Slide∆E= - 4.087x10-19J

∆E = h νλλλλ νννν = c

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Interpretation of the Last Slide’s Results

λλλλ= 486.0 nm

700 nm600 nm500 nm400 nm

This spectral line is due to a 4 2 electron transition

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A Useful Derived Equation∆E= Efinal - Einitial = Einner - Eouter

-2.180x10-18J

ni2

-2.180x10-18J

no2

∆E= -

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Redo the previous problem using this equation

1

ni2

1 no

2∆E= -2.180x10-18J

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Regions of Spectral Lines

1

2

3

4

UV

Lyman series

1

2

3

4

VIS

Balmer series

1

2

3

4

IR

Paschen series

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DeBroglieAssumes that if light (waves) could have par ticle proper ties

then particles could have wave properties

∆E = h ν∆E = mc2

h ν= mc2 h c = mc2

λ λ = h mc

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InterpretationThe wavelength of an electron must be

an integer multiple of the Bohr orbits (quantized)

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Evidence for Wave Nature of the Electron

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Interference Patterns Observed

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Heisenberg Uncertainty Principle

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Schroedinger’s Equation

He combines the mathematics of waves and probability

He constructs 3D probability maps for electrons, called " orbitals"

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Orbitals

"s""p"

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s,p and d orbitals

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Energy Levels, Sub-levels and Orbitals

ENERGY

1

2

3

4

energy level sub-level

1s

2s

2p

3s

3p

3d

4s4p4d4f

orbitals

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Electron Configurations-putting it all together

O8 8 electrons

start with the lowest energy level 1s sublevel is only one in 1st energy levelthe one orbital can hold 2 electrons

this fills the first energy level

next electrons goes in the 2nd energy levelthe s sub-level is lower than ptwo electrons fill the s sublevel

there is a p sublevel in the 2nd energy level

the remaining electrons can go into the p sub-level of the 2nd energy level

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Order of electron filling-first 36 elements (through krypton)

1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p

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“Out of Order”

3s

3p

3d

3rd energy level

4th energy level

4s

4p4d4f

4s

4p4d4f

3s

3p

3d

3rd energy level

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Maximum number of electrons:

1 s 2 s 2 p 3 s 3 p 4 s 3 d 4 p

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Simplifying Electron Configurations

"inert gas core" notation

19K

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Electron Spin-Stern Gerlach Experiment

furnace

Agbeam of gaseous

silver atoms

N

S

powerful magnet

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Electron Spin Pairing

representing paired electrons in an energy diagram

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Energy Diagrams- visualizingelectron configurations

1s 2s 2p

1s

2s 2p

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Example-carbon

1s

2s 2p

6C 1s2 2s2 2p2

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Q5Write electron configurations for Si and Ge

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Q5 cont.Construct energy diagrams for P and F

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Q5 cont.

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Transition Metals

Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn

4s

3d

2 2 2 2 2 2 2 2 2

0 1 2 3 5 6 7 8 10

1

5

1

10

Why the difference?

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Half-filled Sub-levels are More Stable

4s3d

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Problemdo the same for Cu

4s3d

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Magnetic Properties of Atoms

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Quantum Numbers

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Principle Q.N.n

n gives the energy level of the electron

n = 1,2,3,.... (any integer)

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Angular Momentum Q.N.l

the values of l are:

0, 1, ...., n-1

gives the number of sublevels in any energy level

(if n =2, then l= 0 and 1)

meaning:in the second energy level (n=2) there are two sub-levels (s and p)

l sub-level

0 s

1 p

2 d

3 f

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Orientation Quantum Numberml

gives the number of orbitals in a sublevel

ml = -l ....,0,.... +l

if l = 1 (p sub-level)

ml = -1,0,+1 (three p orbitals in the p sub-level)

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Spin Quantum Numberms

tells whether an electron is unpaired (the first into that orbital) or paired

ml = +1/2 for the first electron in an orbital

ml = -1/2 for the paired electron

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How it Works

8O 1s22s22p4

1s

2s 2p

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Q6Provide the four QN's for the characteristic electron of phosphorous

Which element would have the following character isticQN's?

n = 2 l = 1 ml = 0 ms = -1/2