Dr. S. M. Condren Chapter 7 Atomic Structure. Dr. S. M. Condren ELECTROMAGNETIC RADIATION.

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.

Dr. S. M. Condren

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

Dr. S. M. Condren

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

Dr. S. M. Condren

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.

Dr. S. M. Condren

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

Dr. S. M. Condren

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,

Dr. S. M. Condren

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.

Dr. S. M. Condren

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

Dr. S. M. Condren

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

Dr. S. M. Condren

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