Download Presentation
## Chapter 7

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -

**Chapter 7**Atomic Structure Dr. S. M. Condren**ELECTROMAGNETIC RADIATION**Dr. S. M. Condren**Electromagnetic Spectrum**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. Dr. S. M. Condren**Electromagnetic Radiation**Electromagnetic wave • wavelength • frequency • amplitude Dr. S. M. Condren**Electromagnetic Radiation**Figure 7.1 Dr. S. M. Condren**Wave motion: wave length and nodes**Dr. S. M. Condren**Wave Nature of the Electron**Dr. S. M. Condren**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**increasing frequency**increasing wavelength Electromagnetic Radiation Long wavelength --> small frequency Short wavelength --> high frequency Dr. S. M. Condren**Fireworks**Dr. S. M. Condren**Flame Tests**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. Dr. S. M. Condren**Line Emission Spectrum**Dr. S. M. Condren**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**Electromagnetic Radiation**Long wavelength --> small frequency low energy Short wavelength --> high frequency high energy Dr. S. M. Condren**Black Body Radiation**http://www.cbu.edu/~mcondren/C11599/BBvis.mov Dr. S. M. Condren**Photoelectric Effect**Experiment demonstrates the particle nature of light. Dr. S. M. Condren**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**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**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**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**Bohr Atom**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. Dr. S. M. Condren**Energy Adsorption/Emission**Active Figure 7.11 Dr. S. M. Condren**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**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**Origin of Line Spectra**Paschen series Balmer series Active Figure 7.12 Dr. S. M. Condren**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**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**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**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**Types of Orbitals**s orbital p orbital d orbital Dr. S. M. Condren**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**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**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**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**Types of Atomic Orbitals**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 Dr. S. M. Condren**S Orbitals**2s 3s 1s Dr. S. M. Condren**p Orbitals**The three p orbitals lie 90o apart in space Dr. S. M. Condren**2px Orbital**3px Orbital Dr. S. M. Condren**d Orbitals**3dxy Orbital 3dxz Orbital 3dyz Orbital 3dx2- y2 Orbital 3dz2 Orbital Dr. S. M. Condren