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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.
Light with multiple wavelengthsWavelengths separated
refraction
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.
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.
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.
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.
Electron Waves and Orbits
Electrons seemed to be locked into these wave patterns around the nucleus.
Quantum Mechanics
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.
Erwin Schrödinger (1887-1961)
Quantum Numbers and Atomic Orbitals
n = principal quantum number (shell)describes orbital sizespecifies primary energy level
greater n, higher E (like Bohr’s 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
n 1
0n -1
ml = magnetic quantum numberdescribes orbital orientation
the direction is spacealso 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
m
ms 1/2 or
Quantum Numbers and Atomic Orbitals
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 n=2 -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.
Quantum #’s are like an Address.
What do you need to know to find out where you live?
State City Street House
Principle Quantum # (n)
Angular Quantum # (l)
Magnetic Quantum # (ml)
Spin Quantum # (ms)
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.
1s2s2p3s3p4s3d4p5s4d…..
Predicting Orbital Filling
Diagonal Rule
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d 6f
7s 7p 7d 7f
Energy Levels
For H atom All other atoms4s_4p_ _ _ 4d_ _ _ _ _4f _ _ _ _ _ _ _ 4s _
3d _ _ _ _ _
3p _ _ _
3s _ 3p _ _ _ 3d _ _ _ _ _ 3s _
2p _ _ _ (degenerate orbitals)
2s _ 2p _ _ _(degenerate orbitals) 2s _
1s _ 1s _
Inc
EIn
c E
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
A. (3,2,1,+1/2)B. (3,2,-1,+1/2)C. (3,1,1,+1/2)D. (3,2,2,-1/2)E. (3,2,0,+1/2)
Which of the following does not represent a 3d electrons?
What are the atomic numbers of elements
whose outer most electrons are represented by
2p3 and 3p6?
N= 1s22s22p3
Ar=1s22s22p63s23p6