Download - Electronic Structure of Atoms
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Electronic Electronic Structure of AtomsStructure of Atoms
Chapter 6Chemistry 100
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What is light?What is light? Light is obviously real - it is part of our
world. Darkness is the absence of light Light is NOT a solid, a liquid, or even a gas So what is it? It is a form of energy We call it a form of radiant energy
because it carries energy through space
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Electromagnetic radiationElectromagnetic radiation Visible light is a type of electromagnetic
radiation Other types include: infra-red, ultra-violet,
X-rays, gamma rays, radar waves, microwaves, radio and TV waves
Electromagnetic radiation has wave like properties
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WavesWaves
Wavelength (lamda) Frequency (nu) Speed c (see?) = c c = 3.00 108m/s for all
types of electromagnetic radiation.
So how is IR different from UV, for example?
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Electromagnetic SpectrumElectromagnetic Spectrum Different types of electromagnetic
radiation have different wave lengths () and different frequencies ()
Frequency: number of cycles (vibrations) per second. Unit is second-1 or s-1. The Hertz is the SI unit for frequency.
82,000 s-1 is the same as 82 kHz (kiloHertz)
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Units for wavelengthUnits for wavelengthUnit Symbol Length (m) Type of RadiationAngstrom Å 10-10 X-rayNanometre nm 10-9 UV & visibleMicrometre m 10-6 IRMillimetre mm 10-3 IRCentimetre cm 10-2 microwaveMetre m 1 TV, Radio
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Max Planck and his Max Planck and his constant constant hh Suggested that
energy is quantized - comes in small chunks
E = h where n = 1, 2, 3
Compare the potential energy of a brick on a staircase to one on a slope
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Can this be true?Can this be true? We do not find that energy is quantized in
everyday life - h is very small. Cannot see the difference between 200,000,000h and
200,000,001 h Einstein used Planck’s idea to explain the
photoelectric effect For electromagnetic radiation, E = h where is
the frequency of the radiation. High frequency more energy
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What is light?What is light? When we look how light behaves in
experiments with lens, mirrors, etc., we are led to believe that light has wave properties
In the photoelectric effect, light appears to consist of particles - which we call photons
Dual nature of electromagnetic radiation
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Bohr’s AtomBohr’s Atom Bohr said: if energy is quantized then the
energy of an electron in an atom is quantized
So the radius of its orbit cannot be any arbitrary value but must obey the quantum theory. Only certain orbits are allowed
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Allowed Orbitals in Bohr’s Allowed Orbitals in Bohr’s AtomAtom
2
2
220
4
n
22
20
n
nZ
h8meE
...3 ,2 ,1n where nZmehr
The quantity n is a quantum number
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Bohr’s Atom 1913Bohr’s Atom 1913 Electrons move in orbitals with specified
radii Each orbital is associated with a specific
energy This explains why atoms emit (or absorb)
light of well-defined frequency. Examples: the yellow sodium street light and the neon tube.
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Wave BehaviourWave Behaviour Louis de Broglie (1892-1987): If light can
have both wave and particle behaviour, why not wave behaviour for all particles?
= h/m He talked about matter waves
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Matter wavesMatter wavesFind for electron moving at 5.97 106 m/s
rays- Xof wavelength the toSimilar nm122.0m1022.1kg1
g10J1
sm.kg1)s/m1097.5)(g1011.9(
Js1063.6mvh
10
322
629
34
Find for baseball moving at 100 km/h
meaningfulor - measurable be to small tooFar m1065.1hr
s3600km1
m1000kg1
g10J1
sm.kg1)hr/km100)(g145(
Js1063.6mvh
34
32234
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HeisenbergHeisenberg Postulated that there is a limit to how
precisely we can measure both position and momentum
The measurement effects the object being measured
Heisenberg’s Uncertainty Principle
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Schrödinger’s wave Schrödinger’s wave equationequation In 1926, Schrödinger put de Broglie’s
and Heisenberg’s ideas together and came up with the wave equation
The quantity 2 provides information about the electron's position when it has
energy E!
!!equation!ugly truly A EVdxd
m8h
2
2
2
2
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Quantum NumbersQuantum Numbers Schrödinger's wave equation has three
quantum numbers. Principal quantum number n. Has integer values 1,
2, 3 Azimuthal quantum number, l. Allowed values
values of 0, 1... up to n - 1 Magnetic quantum number, ml. Allowed values -l …
0 … +l There is also the Spin quantum number, ms. It
can have a value of -½ or +½
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Atomic orbitalsAtomic orbitals The first shell n = 1 The shell nearest the nucleus l = 0 We call this the s subshell (l = 0) m = 0 There is one orbital in the subshell
s = -½ The orbital can hold two electronss = + ½ one with spin “up”, one “down”
No two electrons in an atom can have the same value for the four quantum numbers: Pauli’s Exclusion Principle
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The second shellThe second shelln = 2 l = 0 or 1 There are two subshells
l = 1 The p subshellm = -1, 0, +1 Three orbitals in the subshells = -½ or + ½ Each orbital can hold 2 electrons.
p subshell can hold 6 electrons
l = 0 The s subshellm = 0 One orbital in the subshells = -½ or + ½ Subshell can hold two electrons
The second shell can hold 8 electrons:
2 in s orbitals and 6 in p orbitals
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If the principal quantum number is n, the shell can hold up to 2n2 electrons
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s Orbitals are Sphericals Orbitals are Spherical
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p Orbitals are Dumbbell p Orbitals are Dumbbell ShapedShaped
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d Orbitals are Complexd Orbitals are Complex
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Aufbau Aufbau PrinciplePrinciple
1s 2s2p 3s 3p 4s3d 4p 5s 4d 5p 6s4f 5d 6p 7s 5f 6d6f
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Let’s do Sodium, Z = 11Let’s do Sodium, Z = 11 Aufbau Principle 1s 2s 2p 3s …. First 2 electrons 1s2 that’s 2 Next 2 electrons 2s2 that’s 4 Six this time 2p6 that’s 10 1 more to go 3s1 that’s all, folks
Electronic configuration of Na is 1s22s22p63s1
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Hund’s RuleHund’s Rule
The configuration with the maximum spin is more stable.
Shall we use1s 2s 2p() () ()()
Or, shall we use1s 2s 2p() () ()()()
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Shorthand Shorthand configurationsconfigurations The configuration of Neon is: 1s22s22p6
Na is 1s22s22p63s1, or in short form: [Ne]3s1 The configuration of Argon:1s22s22p63s23p6
K is: 1s22s22p63s23p64s1, which in short form becomes [Ar]4s1
Note the similarity of the two elements from the same group in the periodic table.The incomplete orbitals are 3s1 and 4s1.
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Same group, similar Same group, similar configurationconfiguration
Fluorine: [He]2s22p5
Chlorine: [Ne]3s23p5
Bromine: [Ar]3d104s24p5
Iodine: [Kr]4d105s25p5
The outer-shell configuration in each case is s2p5
We need not be concerned with the d electrons here because d10 is a filled subshell.
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Electronic Configuration Electronic Configuration & Periodic Table& Periodic Table
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I’m in a spin!!!I’m in a spin!!! Nitrogen has Atomic Number 7 Electronic Configuration: 1s222s22p3
Let’s draw an orbital diagram: