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Dr. S. M. Condren Chapter 7 Atomic Structure

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Dr. S. M. Condren ELECTROMAGNETIC RADIATION

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Dr. S. M. Condren Electromagnetic Spectrum

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Dr. S. M. Condren 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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Dr. S. M. Condren Electromagnetic Radiation Electromagnetic wave wavelength frequency amplitude

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Dr. S. M. Condren Electromagnetic Radiation Figure 7.1

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Dr. S. M. Condren Wave motion: wave length and nodes

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Dr. S. M. Condren Wave Nature of the Electron

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Dr. S. M. Condren Waves have a frequencyWaves have a frequency Use the Greek letter nu,, for frequency, and units are cycles per secUse the Greek letter nu,, for frequency, and units are cycles per sec Use the Greek letter lambda,, for wavelength, and units are metersUse the Greek letter lambda,, for wavelength, and units are meters All radiation:All radiation: = c c = velocity of light = 3.00 x 10 8 m/secc = velocity of light = 3.00 x 10 8 m/sec Long wavelength --> small frequencyLong wavelength --> small frequency Short wavelength --> high frequencyShort wavelength --> high frequency Electromagnetic Radiation

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Dr. S. M. Condren Long wavelength --> small frequency Short wavelength --> high frequency increasing frequency increasing wavelength Electromagnetic Radiation

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Dr. S. M. Condren Fireworks

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Dr. S. M. Condren Flame Tests

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Dr. S. M. Condren 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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Dr. S. M. Condren Line Emission Spectrum

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Dr. S. M. Condren Calculate the frequency, of red light that has a wavelength,, of 700. nm. Example: Calculate the frequency, of red light that has a wavelength,, of 700. nm. = 700. nm)(10 9 nm/1m)(3.00x10 8 m/sec) = 700. nm)(10 9 nm/1m)(3.00x10 8 m/sec) = 4.29x10 14 s -1 = 4.29x10 14 cycles/s = 4.29x10 14 hertz Electromagnetic Radiation

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Dr. S. M. Condren Long wavelength --> small frequency low energy Short wavelength --> high frequency high frequency high energy Electromagnetic Radiation

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Dr. S. M. Condren Black Body Radiation

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Dr. S. M. Condren Experiment demonstrates the particle nature of light. Photoelectric Effect

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Dr. S. M. Condren Energy of Radiation Energy of 1.00 mol of photons of. Energy of 1.00 mol of photons of red light. E = h E = h = (6.63 x Js)(4.29 x s -1 ) = (6.63 x Js)(4.29 x s -1 ) = 2.85 x J per photon = 2.85 x J per photon E per mol = (2.85 x J/ph)(6.02 x ph/mol) (2.85 x J/ph)(6.02 x ph/mol) = kJ/mol = kJ/mol This is in the range of energies that can break bonds.

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Dr. S. M. Condren Spectra Line 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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Dr. S. M. Condren Bohrs greatest contribution to science was in building a simple model of the atom. It was based on an understanding of the of excited atoms. Bohrs greatest contribution to science was in building a simple model of the atom. It was based on an understanding of the SHARP LINE EMISSION SPECTRA of excited atoms. Niels Bohr ( ) Atomic Line Emission Spectra and Niels Bohr

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Dr. S. M. Condren Bohr said classical view is wrong. e - can only exist in certain discrete orbits called. e - can only exist in certain discrete orbits called stationary states. e - is restricted to energy states. e - is restricted to QUANTIZED energy states. Energy of state = - C/n 2 where n = quantum no. = 1, 2, 3, 4,.... Atomic Spectra and Bohr

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Dr. S. M. Condren Bohr Atom

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Dr. S. M. Condren 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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Dr. S. M. Condren Active Figure 7.11 Energy Adsorption/Emission

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Dr. S. M. Condren E = -(3/4)C C has been found from experiment (and is now called, the constant) C has been found from experiment (and is now called R, the Rydberg constant) R (= C) = 1312 kJ/mol or 3.29 x cycles/sec so, E of emitted light = (3/4)R = 2.47 x sec -1 = (3/4)R = 2.47 x sec -1 and = c/ = and = c/ = nm This is exactly in agreement with experiment! Atomic Spectra and Bohr

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Dr. S. M. Condren Visible lines in H atom spectrum are called the series. Visible lines in H atom spectrum are called the BALMER series. High E Short Short High High Low E Long Long Low Low Line Emission Spectra of Excited Atoms

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Dr. S. M. Condren Origin of Line Spectra Balmer series Active Figure 7.12 Paschen series

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Dr. S. M. Condren Bohrs theory was a great accomplishment. Recd Nobel Prize, 1922 Problems with theory Problems with theory theory only successful for H.theory only successful for H. introduced quantum idea artificially.introduced quantum idea artificially. So, we go on to orSo, we go on to QUANTUM or WAVE MECHANICS Niels Bohr ( ) Atomic Line Spectra and Niels Bohr

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Dr. S. M. Condren Schrodinger applied idea of e- behaving as a wave to the problem of electrons in atoms. He developed the WAVE EQUATION Solution gives set of math expressions called Solution gives set of math expressions called WAVE FUNCTIONS, Each describes an allowed energy state of an e - Quantization introduced naturally. E. Schrodinger Quantum or Wave Mechanics

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Dr. S. M. Condren is a function of distance and two angles. Each corresponds to an Each corresponds to an ORBITAL the region of space within which an electron is found. does NOT describe the exact location of the electron. does NOT describe the exact location of the electron. 2 is proportional to the probability of finding an e- at a given point. 2 is proportional to the probability of finding an e- at a given point. WAVE FUNCTIONS,

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Dr. S. M. Condren Uncertainty Principle W. Heisenberg 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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Dr. S. M. Condren Types of Orbitals s orbital p orbital d orbital

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Dr. S. M. Condren Orbitals No more than 2 e - assigned to an orbitalNo more than 2 e - assigned to an orbital Orbitals grouped in s, p, d (and f) subshellsOrbitals grouped in s, p, d (and f) subshells s orbitals d orbitals p orbitals also f orbitals

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Dr. S. M. Condren s orbitals d orbitals p orbitals s orbitals p orbitals d orbitals No.orbs. No. e f orbitals 7 14

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Dr. S. M. Condren The of each orbital is a function of 3 quantum numbers: The shape, size, and energy of each orbital is a function of 3 quantum numbers: (principal) => shell n (principal) => shell (angular) => subshell l (angular) => subshell (magnetic) => designates an orbital within a subshell m l (magnetic) => designates an orbital within a subshell s (spin) s (spin) => designates the direction of spin QUANTUM NUMBERS

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Dr. S. M. Condren SymbolValuesDescription n (principal)1, 2, 3,..Orbital size and energy where E = -R(1/n 2 ) l (angular)0, 1, 2,.. n-1Orbital shape or type (subshell) m l (magnetic)-l..0..+lOrbital orientation # of orbitals in # of orbitals in subshell = 2 l + 1 s (spin)-1/2 or +1/2Direction of spin of electron QUANTUM NUMBERS

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Dr. S. M. Condren Types of Atomic Orbitals

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Dr. S. M. Condren 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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Dr. S. M. Condren S Orbitals 1s 2s3s

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Dr. S. M. Condren The three p orbitals lie 90 o apart in space p Orbitals

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Dr. S. M. Condren 2p x Orbital 3p x Orbital

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Dr. S. M. Condren d Orbitals 3dxy Orbital 3dxz Orbital 3dyz Orbital 3dx2- y2 Orbital 3dz2 Orbital

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