C. Johannesson I. Waves & Particles (p ) Ch. 4 - Electrons in Atoms

Wave Description of Light zElectromagnetic spectrum: composed of visible light and all other forms of electromagnetic radiation zAll appears to behave like waves zSpeed: 3.0 X 10 8 m/sec C. Johannesson

A. Waves zWavelength ( ) - length of one complete wave yUnit: m, cm, nm zFrequency ( ) - # of waves that pass a point during a certain time period yhertz (Hz) = 1/s

C. Johannesson B. EM Spectrum zFrequency & wavelength are inversely proportional c = c:speed of light (3.00  10 8 m/s) :wavelength (m, nm, etc.) :frequency (Hz)

yInverse Proportional Relationship xAs increases, frequency decreases xAs decreases, frequency increases C. Johannesson

A. Waves A greater amplitude (intensity) greater frequency (color) crest origin trough A

C. Johannesson B. EM Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY

C. Johannesson B. EM Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY ROYG.BIV redorangeyellowgreenblueindigoviolet

Photoelectric Effect z1 st experiment to oppose the wave theory of light zBased on the emission of electrons when light shines on metals zFound that light had to be a certain frequency to cause emission C. Johannesson

C. Quantum Theory zPlanck (1900) yObserved - emission of light from hot objects yConcluded - energy is emitted in small, specific amounts (quanta) yQuantum - minimum amount of energy change

C. Johannesson C. Quantum Theory zPlanck (1900) vs. Classical TheoryQuantum Theory

C. Johannesson C. Quantum Theory E:energy (J, joules) h:Planck’s constant (  J·s) :frequency (Hz) E = h zThe energy of a photon is proportional to its frequency.

C. Johannesson C. Quantum Theory zEinstein (1905) yObserved - photoelectric effect

C. Johannesson C. Quantum Theory zEinstein (1905) yConcluded - light has properties of both waves and particles “wave-particle duality”

Einstein zEach particle has a quantum of energy zParticles are called photons zE photon = hv zElectromagnetic radiation is absorbed by matter only in whole-numbers of photons zFor a electron to be emitted, it must be struck by a photon C. Johannesson

zAtoms: found naturally in the ground state yAddition of energy could cause them to go to the excited state yWhen atoms fall from the excited state back to the ground state energy is given off in the form electromagnetic radiation C. Johannesson

A. Line-Emission Spectrum ground state excited state ENERGY IN PHOTON OUT

zProduced 3 series of light yLyman series: Ultraviolet Light yBalmer series: visible light yPaschen series: infrared light C. Johannesson

zScientists predicted a continuous spectrum of light yEnded up with the quantum theory (using excited hydrogen atom) x1. Excited atoms emitted specific frequency of light x2. the energy differences from the excited to ground state were fixed xElectron only exists in specific energy states C. Johannesson

Bohr model zNiels Bohr zElectron circles the nucleus only in allowed paths called orbits yIn this orbit, the electron has a definite or fixed energy yLowest energy state is closest to the nucleus yHighest energy state is furthest from the nucelus C. Johannesson

ySpectral lines = energy levels yWhile in orbit, electrons cannot gain or lose energy yElectrons can move to higher energy levels by gaining energy xThe energy is equal to the difference in the higher and lower orbits C. Johannesson

zGoing from the higher energy to the lower energy causes the emission of a photon of energy equal to the energy difference C. Johannesson

B. Bohr Model zEnergy of photon depends on the difference in energy levels zBohr’s calculated energies matched the IR, visible, and UV lines for the H atom

C. Johannesson C. Other Elements zEach element has a unique bright-line emission spectrum. y“Atomic Fingerprint” Helium

Problems zDid not explain the spectra of atoms with more than one electron zDid not explain the chemical behavior of atoms C. Johannesson

QUANTUM MODEL OF THE ATOM Section 2 C. Johannesson

Quantum Model zDual wave-particle theory zDeBroglie yElectrons should be considered waves confined to a space that can only have certain frequencies yElectrons can be bent or diffracted yElectrons can interfere with each other C. Johannesson

A. Electrons as Waves EVIDENCE: DIFFRACTION PATTERNS ELECTRONS VISIBLE LIGHT

Heisenburg zSaid it was impossible to determine both the position and velocity of an electron C. Johannesson

Schrodinger zQuantization of electrons was confirmed zQuantum Theory describes mathematically the wave properties of electrons and other small particles zElectrons do not travel in neat orbits yExist in regions called orbitals yThese are three-dimensional regions C. Johannesson