Arrangement of Arrangement of Electrons in AtomsElectrons in Atoms

Development of a New Atomic Development of a New Atomic ModelModel

Wave Description Of Wave Description Of LightLight Electromagnetic Radiation:Electromagnetic Radiation:

form of energy that exhibits wavelike form of energy that exhibits wavelike behavior as it travels through space.behavior as it travels through space.

EX: visible light, X-ray, Ultraviolet and EX: visible light, X-ray, Ultraviolet and inferred light, microwaves, and radio waves.inferred light, microwaves, and radio waves.

Travels at a constant speed of Travels at a constant speed of 3.0 x 103.0 x 1088 m/s m/s Electromagnetic Spectrum:Electromagnetic Spectrum: All the All the

electromagnetic radiation form the ES. electromagnetic radiation form the ES. (fig 4-1, p. 92)(fig 4-1, p. 92)

Electromagnetic SpectrumElectromagnetic Spectrum

Wave CalculationsWave Calculations

Wavelength (Wavelength (λλ)) - distance between two - distance between two peaks . Measured in meterspeaks . Measured in meters

Frequency (v)Frequency (v) - number of peaks that - number of peaks that pass a point each second.pass a point each second. Hz = Hertz = sHz = Hertz = s-1-1

c = c = λλ v  v              where c = 3.0 x 10where c = 3.0 x 1088 m/s m/s

Is light really a wave? Is light really a wave?

Max PlanckMax Planck – – did experiments with light-matter did experiments with light-matter interactions where light did not act like a waveinteractions where light did not act like a wave

Photoelectric EffectPhotoelectric Effect - - emission of electrons emission of electrons from a metal when light shines on the metal.from a metal when light shines on the metal. Only emitted at certain energies; wave theory said Only emitted at certain energies; wave theory said

any energy should do it. any energy should do it.

Led to the particle theory of lightLed to the particle theory of light

Planck suggested that objects emit energy Planck suggested that objects emit energy in specific amounts called QUANTAin specific amounts called QUANTA

QuantumQuantum - minimum quantity of energy that - minimum quantity of energy that can be lost or gained by an atom. can be lost or gained by an atom.

led Planck to relate the energy of an electron led Planck to relate the energy of an electron with the frequency of EMR            with the frequency of EMR            

E = hv E = hv                     E= Energy (J, of a quantum of radiation) E= Energy (J, of a quantum of radiation) v= frequency of radiation emitted v= frequency of radiation emitted h= Planck’s constant (6.626 x 10h= Planck’s constant (6.626 x 10-34-34 J∙s) J∙s)

Equation PracticeEquation Practice What is the frequency of yellow light with a What is the frequency of yellow light with a

wavelength of 548 nm?wavelength of 548 nm?

Equation PracticeEquation Practice What is the wavelength of blue light with a What is the wavelength of blue light with a

frequency of 4.60 x 10frequency of 4.60 x 102323 Hz? Hz?

Equation PracticeEquation Practice What is the energy of magenta light with a What is the energy of magenta light with a

wavelength of 691 nm?wavelength of 691 nm?

leads to leads to Einstein’sEinstein’s dual nature of light (EMR dual nature of light (EMR behaves as both a wave and a particle) behaves as both a wave and a particle)

PhotonPhoton - particle of EMR having zero mass and - particle of EMR having zero mass and carrying a quantum of energy.carrying a quantum of energy.

Hydrogen Emission SpectrumHydrogen Emission Spectrum Ground State Ground State - Lowest energy state of electron.- Lowest energy state of electron. Excited StateExcited State - higher energy than ground state. - higher energy than ground state. Bright-line SpectrumBright-line Spectrum (emission spectrum) (emission spectrum)

Series of specific light frequencies emitted by Series of specific light frequencies emitted by elements elements

"spectra are the fingerprints of the elements""spectra are the fingerprints of the elements"

The Development of A The Development of A New Atomic ModelNew Atomic Model

Rutherford’s model was an improvement Rutherford’s model was an improvement over previous models, but still over previous models, but still incomplete.incomplete. Where exactly are electrons located?Where exactly are electrons located? What prevented the electrons from being What prevented the electrons from being

drawn into the nucleus?drawn into the nucleus?

Bohr Model Of H AtomBohr Model Of H Atom Bohr explained how the electrons Bohr explained how the electrons

stay in the cloud instead of stay in the cloud instead of slamming into the nucleusslamming into the nucleus

Definite orbits; paths Definite orbits; paths The greater the distance from the The greater the distance from the

nucleus, the greater the energy of nucleus, the greater the energy of an electron in that shell. an electron in that shell.

Electrons start in lowest possible level - Electrons start in lowest possible level - ground stateground state..

Absorb energyAbsorb energy - become excited and shift - become excited and shift upward. upward.

Dropping back downDropping back down - emits photons - emits photons (packets of energies equal to the previously (packets of energies equal to the previously absorbed energy).absorbed energy).

Hydrogen Emission Spectrum

Quantum Model of the AtomQuantum Model of the Atom Bohr’s model was great, but it didn’t Bohr’s model was great, but it didn’t

answer the question “why?”answer the question “why?” Why did electrons have to stay in specific Why did electrons have to stay in specific

orbits?orbits? Why couldn’t the electrons exist anywhere Why couldn’t the electrons exist anywhere

within the electron cloud?within the electron cloud?

Louis de Broglie pointed out that Louis de Broglie pointed out that electrons act like waveselectrons act like waves Using Planck’s equation (E=hv), dB proved Using Planck’s equation (E=hv), dB proved

that electrons can have specific energies and that electrons can have specific energies and that Bohr’s quantized orbits were actually that Bohr’s quantized orbits were actually correctcorrect

Heisenberg Uncertainty Heisenberg Uncertainty PrinciplePrinciple

Impossible to determine both the exact Impossible to determine both the exact location and velocity of an electronlocation and velocity of an electron

Schrodinger Wave Schrodinger Wave EquationEquation

He gave more support to Bohr’s He gave more support to Bohr’s quantized energy levelsquantized energy levels

Quantum theory – describes the wave Quantum theory – describes the wave properties of electrons using properties of electrons using mathematical equationsmathematical equations

Disproved Bohr’s “train tracks” within Disproved Bohr’s “train tracks” within those energy levelsthose energy levels