Ch. 7 Atomic and Electronic Structure. Electromagnetic Radiation and Atomic Spectra 1. Electromagnetic Radiation -- Light wavelength: l (m) frequency: n (Hz = s –1 ) ln = c = speed of light = 3.00 x 10 8 m/s. memorize!. memorize!. Wave/Particle Duality.
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Electromagnetic Radiation and Atomic Spectra
1. Electromagnetic Radiation -- Light
wavelength: l (m) frequency:n (Hz = s–1)
ln = c = speed of light = 3.00 x 108 m/s
l = h/mv
where l = wavelength, h = Planck’s constant
(6.626 x 10–34 J•s), m = mass,
v = velocity
Energetically excited atoms only emit radiation in discrete energies corresponding to the atom’s electronic energy levels.
where b = 2.18 x 10–18 J
– Where n is a “quantum number”
with possible values of n = 1,2,3,4,…
– Increasing value of n indicates an
electron “orbit” farther from the nucleus
It is possible to calculate energy differences between levels (i.e. the atomic spectrum) with different n values by using the Rydberg Equation -- see textbook (but don’t memorize!)
Heisenberg’s Uncertainty Principle states
Dx • mDv = h/4p(do not memorize)
where Dx is the uncertainty in the position and Dv is the uncertainty in the velocity, m = mass, h = Planck’s constant
This says that electrons cannot be precisely located and their velocity known at the same time. However, the probability of an electron being in a location can be related to its energy using the
HY = EY
where H = hamiltonian operator, E = energy, and Y = wavefunction
shells ---> subshells ---> orbitals
e.g. within a subshell having l = 2, there are 5 orbitals corresponding to the 5 possible values of ml (-2, -1, 0, +1, +2)
Atomic orbitals are best viewed as “clouds of electron density” and represented as contour plots of the probability of finding the electron.
nodal surface an imaginary point, plane, or spherical surface where the probability of finding the electron is equal to zero
s orbitals are spherical shaped
p orbitals are “bow tie” shaped and oriented along the coordinate axes
d orbitals have more complex shapes
Orbital Phases –phases alternate just like in 2-D waves; always draw orbitals with “shaded” and “unshaded” lobes. (will be important in bonding)