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Chapter 7. Atomic Structure. ELECTROMAGNETIC RADIATION. Electromagnetic Spectrum. Electromagnetic Radiation. Electromagnetic wave

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Chapter 7

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    1. Chapter 7 Atomic Structure Dr. S. M. Condren


    3. Electromagnetic Spectrum Dr. S. M. Condren

    4. 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

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

    6. Electromagnetic Radiation Figure 7.1 Dr. S. M. Condren

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

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

    9. Electromagnetic Radiation • Waves have a frequency • Use the Greek letter “nu”, , for frequency, and units are “cycles per sec” • Use the Greek letter “lambda”, l, for wavelength, and units are “meters” • All radiation:  •  = c • c = velocity of light = 3.00 x 108 m/sec • Long wavelength --> small frequency • Short wavelength --> high frequency Dr. S. M. Condren

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

    11. Fireworks Dr. S. M. Condren

    12. Flame Tests Dr. S. M. Condren

    13. 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. Dr. S. M. Condren

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

    15. Electromagnetic Radiation Example:Calculate the frequency, n, of red light that has a wavelength, l, of 700. nm. • = (1/700. nm)(109nm/1m)(3.00x108m/sec) =4.29x1014 s-1 = 4.29x1014 cycles/s = 4.29x1014 hertz Dr. S. M. Condren

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

    17. Black Body Radiation Dr. S. M. Condren

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

    19. Energy of Radiation Energy of 1.00 mol of photons of red light. E = h• = (6.63 x 10-34 J•s)(4.29 x 1014 s-1) = 2.85 x 10-19 J per photon E per mol = (2.85 x 10-19 J/ph)(6.02 x 1023 ph/mol) = 171.6 kJ/mol This is in the range of energies that can break bonds. Dr. S. M. Condren

    20. 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. Dr. S. M. Condren

    21. Atomic Line Emission Spectra and Niels Bohr Bohr’s greatest contribution to science was in building a simple model of the atom. It was based on an understanding of theSHARP LINE EMISSION SPECTRAof excited atoms. Niels Bohr (1885-1962) Dr. S. M. Condren

    22. Atomic Spectra and Bohr Bohr said classical view is wrong. e- can only exist in certain discrete orbits — called stationary states. e- is restricted to QUANTIZED energy states. Energy of state = - C/n2 where n = quantum no. = 1, 2, 3, 4, .... Dr. S. M. Condren

    23. Bohr Atom Dr. S. M. Condren

    24. 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. Dr. S. M. Condren

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

    26. Atomic Spectra and Bohr ∆E = -(3/4)C C has been found from experiment (and is now called R, the Rydberg constant) R (= C) = 1312 kJ/mol or 3.29 x 1015 cycles/sec so, E of emitted light = (3/4)R = 2.47 x 1015 sec-1 and l = c/n = 121.6 nm This is exactly in agreement with experiment! Dr. S. M. Condren

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

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

    29. Atomic Line Spectra and Niels Bohr Bohr’s theory was a great accomplishment. Rec’d Nobel Prize, 1922 Problems with theory — • theory only successful for H. • introduced quantum idea artificially. • So, we go on to QUANTUM or WAVE MECHANICS Niels Bohr (1885-1962) Dr. S. M. Condren

    30. Quantum or Wave Mechanics 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 WAVE FUNCTIONS,  Each describes an allowed energy state of an e- Quantization introduced naturally. E. Schrodinger 1887-1961 Dr. S. M. Condren

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

    32. Uncertainty Principle • 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. W. Heisenberg 1901-1976 Dr. S. M. Condren

    33. Types of Orbitals s orbital p orbital d orbital Dr. S. M. Condren

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

    35. s orbitals p orbitals d orbitals f orbitals d orbitals f orbitals s orbitals p orbitals 7 No. orbs. 1 3 5 No. e- 14 2 6 10 Dr. S. M. Condren

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

    37. QUANTUM NUMBERS Symbol Values Description n (principal) 1, 2, 3, .. Orbital size and energy where E = -R(1/n2) l (angular) 0, 1, 2, .. n-1 Orbital shape or type (subshell) ml (magnetic) -l..0..+l Orbital orientation # of orbitals in subshell = 2 l + 1 s (spin) -1/2 or +1/2 Direction of spin of electron Dr. S. M. Condren

    38. Types of Atomic Orbitals Dr. S. M. Condren

    39. 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 Dr. S. M. Condren

    40. S Orbitals 2s 3s 1s Dr. S. M. Condren

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

    42. 2px Orbital 3px Orbital Dr. S. M. Condren

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