Atomic spectra,

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Atomic spectra, Quantum Numbers and Atomic
Orbitals
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Atomic Spectra
A spectroscope is an instrument that disperses
the light emitted by an excited gas into the
different frequencies the light contains.
refraction
Light with multiple wavelengths
Wavelengths separated
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Atomic Spectra
An emission spectrum consists of the various
frequencies of light given off by an excited
substance. Below is the part of the emission
spectra of sodium.
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Atomic Spectra
An absorption spectrum consists of the various
frequencies absorbed by a substance when white
light is passed through it. The frequencies in
the spectrum of an element fall into sets called
spectral series. Seen here is the spectral series
of hydrogen.
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Origin of Absorption Spectra
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Spectrum of hydrogen

• When energy is supplied to the H gas sample,
  individual atoms absorb different amount of
  energy and electron shift to different energy
  levels, I,e., 3rd, 4th, 5th.
• The electrons are in higher energy levels are
  relatively unstable and drop back to lower energy
  levels.

• This process of dropping back, energy is emitted
  in the form of line spectrum containing various
  lines of particular frequency and wavelength.

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Spectrum of Hydrogen
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Electron Waves and Orbits
An electron can circle a nucleus only in orbits
that contain a whole number of de Broglie
Wavelengths. The quantum number n of an orbit is
the number of electron waves that fit into the
orbit.
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Electron Waves and Orbits
Electrons seemed to be locked into these wave
patterns around the nucleus.
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Quantum Mechanics
Erwin Schrödinger (1887-1961)
The theory of quantum mechanics was developed by
Erwin Schrödinger, Werner. According to quantum
mechanics, the position and momentum of a
particle cannot both be accurately known at the
same time. Only its most probable position or
momentum can be determined.
The most probable distance between the proton and
electron for a hydrogen atom turns out to be
about 0.89Å, the same as Niels Bohr.
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Quantum Numbers and Atomic Orbitals

• n principal quantum number (shell)
• describes orbital size
• specifies primary energy level
• greater n, higher E (like Bohrs E)
• l angular momentum quantum number
  (subshell)(azimuthal quantum number)
• describes orbital shape l 0 s orbital
• l 1 p orbital inc E
• l 2 d orbital within
• l 3 f orbital n

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Quantum Numbers and Atomic Orbitals

• ml magnetic quantum number
• describes orbital orientation
• the direction is space
• also tells the number of orbitals of same
  energy (degenerate orbitals)
• So, the combination of n, l, and ml, completely
  describes a specific orbital, its size , shape
  and orientation.
• To make a complete picture, a 4th quantum number
  added, ms.
• ms spin quantum number - describes the electron
  spin in the orbital

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Quantum Numbers
principal quantum number n
1,2,3,.. orbital quantum number l
0,1,2,.n-1 magnetic quantum number m -l to l
for n2 -2,-1,0,1,2spin magnetic quantum
number ½ or ½ spin Its like your address. To
find where you are you need to know 4 things
state, city, street, house . To know where or
what state the electron is in you need to know
the four quantum numbers.
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Quantum s are like an Address.
What do you need to know to find out where you
live?
State
City
Street
House
Magnetic Quantum (ml)
Spin Quantum (ms)
Principle Quantum (n)
Angular Quantum (l)
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Shapes of Atomic Orbitals
P orbital
s orbital
d orbital
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Quantum Numbers
3py
3d
2py
1s
3s
2s
2px
3px
3pz
2pz
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s and p orbital
Movie
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d orbital
Movie
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Aufbau Principle

• For an atom in its ground state ( the lowest
  energy
• configuration) fill the lowest energy orbital
  first
• then go up in energy until all the electrons
  are used.

1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p
6d 6f 7s 7p 7d 7f
Predicting Orbital Filling
Diagonal Rule
1s2s2p3s3p4s3d4p5s4d..
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Energy Levels

• For H atom All other atoms
• 4s_4p_ _ _ 4d_ _ _ _ _4f _ _ _ _ _ _ _ 4s _
• 3d _ _ _ _ _
• 3p _ _ _
• 3s _ 3p _ _ _ 3d _ _ _ _ _ 3s _
• 2p _ _ _ (degenerate orbitals)
• 2s _ 2p _ _ _(degenerate orbitals) 2s _
• 1s _ 1s _

Inc E
Inc E
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Pauli Exclusion Principle

• No two electrons in the same atom can have the
  same four quantum numbers
• Each electron has a unique address
• Designated by a set of quantum numbers (n, l ,ml
  , ms)
• So (1,0,0, 1/2) indicates an electron in a 1s
  orbital
• While (3,1, -1, 1/2) would be a 3p electron

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Which of the following does not represent a 3d
electrons?

1. (3,2,1,1/2)
2. (3,2,-1,1/2)
3. (3,1,1,1/2)
4. (3,2,2,-1/2)
5. (3,2,0,1/2)

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What are the atomic numbers of elements whose
outer most electrons are represented by 2p3 and
3p6?
N 1s22s22p3
Ar1s22s22p63s23p6
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