Quantum numbers
n
principal
m1
magnetic
l
angular momentum
ms
spin
Value of n
Value of l
Value of m1
Type of
atomic orbital
Number of
orbitals
1
0
0
1s
1
2
0
0
2s
1
2
1
-1, 0, +1
2p
3
3
0
0
3s
1
3
1
-1, 0, +1
3p
3
3
2
-2, -1, 0, +1, +2
3d
5
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Pauli Exclusion Principle
No 2 electrons in any one atom can have the same set of
four quantum numbers
• the maximum number of electrons in any orbital is 2
• 2 electrons occupying the same orbital must have opposite spin
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Electronic configuration
H 1s1 or
1s
He 1s2 or
1s
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Aufbau principle
• Lowest energy orbitals filled first
• Electrons assigned to orbitals in order of increasing n + l
• Where 2 subshells have same n + l, that with lowest n filled first
Hund’s rule of maximum multiplicity
Degenerate orbitals occupied singly, with electrons keeping their spin
parallel before spin pairing occurs
N 1s2 2s2 2p3
1s
2s
2p
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Electronic arrangement of Noble gases
Ne 1s2 2s2 2p6
Ar 1s2 2s2 2p6 3s2 3p6
Electronic configuration of other elements can be abbreviated
taking account of previous Noble gas
e.g. magnesium [Ne] 3s2
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Periodic table blocks
Periodic table subdivided into s, p, d and f blocks
depending on which subshell occupied by outermost electrons
s-block
d-block
Na 1s2 2s2 2p6 3s1
f-block
p-block
N 1s2 2s2 2p3
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Ionisation energies
E (g)
E+ (g)
E+ (g) + eE2+ (g) + e-
Three main factors affecting ionisation energies
• atomic size - the bigger the smaller!
• nuclear charge - the bigger the bigger!
• screening effect - the bigger the smaller!
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First ionisation energies
He 1s2
Ne 1s2 2s2 2p6
Ar 1s2 2s2 2p6 3s2 3p6
In general,
across a period … ionisation energy increases
down a group …. ionisation energy decreases
Be 1s2 2s2
N 1s2 2s2 2p3
B 1s2 2s2 2p1
O 1s2 2s2 2p4
Second and third
ionisation energies?
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Spectroscopy
Spectral lines correspond to transitions between energy levels
Lines usually in visible of UV region of electromagnetic spectrum
Atomic emission spectroscopy
• gaseous sample excited with
thermal or electrical energy
• qualitative and quantitative intensity of radiation increases
with amount of element
• helium discovered using this
technique - Sir Norman Lockyer
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Spectroscopy
• radiation passed through
gaseous sample of substance
• qualitative and quantitative absorbance proportional to
concentration of element
Atomic absorption spectroscopy
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Atomic absorption spectroscopy
Calibration curve
80
A bs or banc e
60
40
20
0
0
10
20
30
40
50
60
Concentration
Allows determination of concentrations of elements in samples
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