Dr. S. M. Condren Chapter 7 Atomic Structure
Mar 26, 2015
Dr. S. M. Condren
Chapter 7
Atomic Structure
Dr. S. M. Condren
ELECTROMAGNETIC RADIATION
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Electromagnetic Spectrum
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Electromagnetic Radiation
Electromagnetic wave• A wave of energy having a frequency
within the electromagnetic spectrum and propagated as a periodic disturbance of the electromagnetic field when an electric charge oscillates or accelerates.
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Electromagnetic Radiation
Electromagnetic wave
• wavelength
• frequency
• amplitude
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Electromagnetic RadiationElectromagnetic Radiation
Figure 7.1Figure 7.1
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Wave motion: wave length and nodesWave motion: wave length and nodes
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Wave Nature of the Electron
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• Waves have a frequencyWaves have a frequency• Use the Greek letter “nu”, Use the Greek letter “nu”, , for frequency, and , for frequency, and
units are “cycles per sec”units are “cycles per sec”• Use the Greek letter “lambda”, Use the Greek letter “lambda”, , for , for
wavelength, and units are “meters”wavelength, and units are “meters”
• All radiation: All radiation: • = c• c = velocity of light = 3.00 x 10c = velocity of light = 3.00 x 1088 m/sec m/sec• Long wavelength --> small frequencyLong wavelength --> small frequency• Short wavelength --> high frequencyShort wavelength --> high frequency
Electromagnetic Radiation
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Long wavelength --> small frequencyLong wavelength --> small frequency
Short wavelength --> high frequencyShort wavelength --> high frequency
increasing increasing frequencyfrequency
increasing increasing wavelengthwavelength
Electromagnetic Radiation
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Fireworks
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Flame Tests
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The Electric Pickle
• Excited atoms can emit light.
• Here the solution in a pickle is excited electrically. The Na+ ions in the pickle juice give off light characteristic of that element.
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Line Emission Spectrum
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Example: Calculate the frequency, Calculate the frequency, of of red light that has a wavelength, red light that has a wavelength, , of , of 700. nm.700. nm. ==700. nm)(10700. nm)(1099nm/1m)(3.00x10nm/1m)(3.00x1088m/sec)m/sec)
==4.29x104.29x1014 14 ss-1-1
= 4.29x10= 4.29x1014 14 cycles/scycles/s
= 4.29x10= 4.29x1014 14 hertzhertz
Electromagnetic Radiation
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Long wavelength -->
small frequency
low energy
Short wavelength --> Short wavelength --> high frequencyhigh frequency
high energyhigh energy
Electromagnetic Radiation
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Black Body Radiation
http://www.cbu.edu/~mcondren/C11599/BBvis.mov
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Experiment demonstrates the particle nature of light.Experiment demonstrates the particle nature of light.Experiment demonstrates the particle nature of light.Experiment demonstrates the particle nature of light.
Photoelectric Effect
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Energy of RadiationEnergy of 1.00 mol of photons of Energy of 1.00 mol of photons of red light..
E = h•E = h•
= (6.63 x 10= (6.63 x 10-34-34 J•s)(4.29 x 10 J•s)(4.29 x 101414 s s-1-1))
= 2.85 x 10= 2.85 x 10-19-19 J per photon J per photon
E per mol = E per mol =
(2.85 x 10(2.85 x 10-19-19 J/ph)(6.02 x 10 J/ph)(6.02 x 102323 ph/mol) ph/mol)
= 171.6 kJ/mol= 171.6 kJ/mol
This is in the range of energies that can break This is in the range of energies that can break bonds.bonds.
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SpectraLine Spectrum• A spectrum produced by a luminous gas or
vapor and appearing as distinct lines characteristic of the various elements constituting the gas.
Emission Spectrum• The spectrum of bright lines, bands, or
continuous radiation characteristic of and determined by a specific emitting substance subjected to a specific kind of excitation.
Absorption Spectrum• Wavelengths of light that are removed from
transmitted light.
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Bohr’s greatest contribution Bohr’s greatest contribution to science was in building to science was in building a simple model of the a simple model of the atom. It was based on an atom. It was based on an understanding of theunderstanding of the SHARP LINE EMISSION SPECTRA of excited atoms.of excited atoms.
Niels BohrNiels Bohr
(1885-1962)(1885-1962)
Atomic Line Emission Spectraand Niels Bohr
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Bohr said classical view is wrong. Bohr said classical view is wrong.
ee-- can only exist in certain discrete can only exist in certain discrete orbits — called orbits — called stationary states. .
ee-- is restricted to is restricted to QUANTIZED energy energy states.states.
Energy of state = - C/n2
where n = quantum no. = 1, 2, 3, 4, ....where n = quantum no. = 1, 2, 3, 4, ....
Atomic Spectra and Bohr
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Bohr Atom
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Energy States
Ground State• The state of least possible energy in a
physical system, as of elementary particles. Also called ground level.
Excited States
• Being at an energy level higher than the ground state.
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Active Figure 7.11Active Figure 7.11
Energy Adsorption/Emission
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∆E = -(3/4)C
C has been found from experiment (and is now C has been found from experiment (and is now called called R, the , the Rydberg constant) constant)
R (= C) = 1312 kJ/mol or 3.29 x 10R (= C) = 1312 kJ/mol or 3.29 x 101515 cycles/sec cycles/sec
so, E of emitted lightso, E of emitted light
= (3/4)R = 2.47 x 10= (3/4)R = 2.47 x 101515 sec sec-1-1
and and = c/ = c/ = = 121.6 nmThis is exactly in agreement with experiment!
.
n = 1
n = 2E = -C (1/ 22)
E = -C (1/ 12)
E N E R G Y
.
n = 1
n = 2E = -C (1/ 22)
E = -C (1/ 12)
E N E R G Y
Atomic Spectra and
Bohr
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Visible lines in H atom spectrum are Visible lines in H atom spectrum are called the called the BALMER series. series.
High EHigh EShort Short High High
Low ELow ELong Long Low Low
Line Emission Spectra of Excited Atoms
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Origin of Line Spectra
Balmer seriesBalmer series
Active Figure 7.12Active Figure 7.12
Paschen series
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Bohr’s theory was a great Bohr’s theory was a great accomplishment.accomplishment.
Rec’d Nobel Prize, 1922Rec’d Nobel Prize, 1922
Problems with theory —Problems with theory —• theory only successful for H.theory only successful for H.• introduced quantum idea introduced quantum idea
artificially.artificially.• So, we go on to So, we go on to QUANTUM or or
WAVE MECHANICSNiels BohrNiels Bohr
(1885-1962)(1885-1962)
Atomic Line Spectraand Niels Bohr
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Schrodinger applied idea of e- Schrodinger applied idea of e- behaving as a wave to the problem behaving as a wave to the problem of electrons in atoms.of electrons in atoms.
He developed the He developed the WAVE WAVE EQUATIONEQUATION
Solution gives set of math Solution gives set of math expressions called expressions called WAVE
FUNCTIONS, Each describes an allowed energy Each describes an allowed energy
state of an estate of an e--
Quantization introduced naturally.
E. SchrodingerE. Schrodinger1887-19611887-1961
Quantum or Wave Mechanics
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•is a function of distance and two is a function of distance and two angles.angles.
• • Each Each corresponds to an corresponds to an
ORBITAL — the region of space within which an electron is found.
• • does NOT describe the exact does NOT describe the exact location of the electron.location of the electron.
• • 22 is proportional to the probability is proportional to the probability of finding an e- at a given point.of finding an e- at a given point.
WAVE FUNCTIONS,
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Uncertainty Principle
W. HeisenbergW. Heisenberg1901-19761901-1976
•Problem of defining nature of electrons solved by W. Heisenberg.•Cannot simultaneously define the position and momentum (=m*v) of an electron.•We define e- energy exactly but accept limitation that we do not know exact position.
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Types of Orbitals
s orbitals orbital p orbitalp orbital d orbitald orbital
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Orbitals• No more than 2 eNo more than 2 e-- assigned to an orbital assigned to an orbital• Orbitals grouped in s, p, d (and f) subshellsOrbitals grouped in s, p, d (and f) subshells
s orbitalss orbitals
d orbitalsd orbitals
p orbitalsp orbitalsalso
f orbitals
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s orbitalss orbitals
d orbitalsd orbitals
p orbitalsp orbitals
s orbitalss orbitals p orbitalsp orbitals d orbitalsd orbitals
No.No.orbs.orbs.
No. e-No. e-
11 33 55
22 66 1010
f orbitalsf orbitals
77
1414
f orbitals
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The The shape, size, and energy of each orbital is of each orbital is a function of 3 quantum numbers:a function of 3 quantum numbers:
n (principal)(principal) => shell=> shell
l (angular) (angular) => subshell=> subshell
ml (magnetic)(magnetic) => designates an orbital => designates an orbital within a subshellwithin a subshell
s (spin)s (spin) => designates the direction of spin
QUANTUM NUMBERS
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SymbolSymbol ValuesValues DescriptionDescription
n (principal)n (principal) 1, 2, 3, ..1, 2, 3, .. Orbital size and energy Orbital size and energy where E = -where E = -
R(1/nR(1/n22))l (angular)l (angular) 0, 1, 2, .. n-10, 1, 2, .. n-1 Orbital shape or type Orbital shape or type
(subshell) (subshell)
mmll (magnetic) (magnetic) -l..0..+l-l..0..+l Orbital orientationOrbital orientation
# of orbitals in # of orbitals in subshell = 2 l + 1subshell = 2 l + 1
s (spin)s (spin) -1/2 or +1/2-1/2 or +1/2 Direction of spin of electronDirection of spin of electron
QUANTUM NUMBERSQUANTUM NUMBERS
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Types of Atomic Orbitals
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Atomic Orbitals
• Types of orbitals found in the known elements: s, p, d, and f
• schools play defensive football
• Packer version: secondary pass defense fails
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S Orbitals
1s 2s 3s
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The three p orbitals lie 90The three p orbitals lie 90oo apart in space apart in space
p Orbitals
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2p2pxx Orbital Orbital 3px Orbital
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d Orbitals3dxy Orbital3dxy Orbital 3dxz Orbital3dxz Orbital 3dyz Orbital3dyz Orbital
3dx2- y2 Orbital3dx2- y2 Orbital 3dz2 Orbital3dz2 Orbital