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

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

Black Body Radiation http://www.cbu.edu/~mcondren/C11599/BBvis.mov Dr. S. M. Condren

Experiment demonstrates the particle nature of light. 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 the SHARP LINE EMISSION SPECTRA of excited atoms. Niels Bohr (1885-1962) Dr. S. M. Condren

Energy of state = - C/n2 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 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 High E Short  High  Low E Long  Low  Visible lines in H atom spectrum are called the BALMER series. Dr. S. M. Condren

Origin of Line Spectra Balmer series Active Figure 7.12 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 s orbitals p orbitals d orbitals f 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

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

n (principal) => shell l (angular) => subshell 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

Symbol Values Description 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 1s 2s 3s Dr. S. M. Condren

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

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

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