Chapter 5
Electronic Configurations
and the Periodic Table
5.1 Relative Energies of Orbitals
5.2 Electronic Configurations of Elements
5.3 The Periodic Table
5.4 Ionization Enthalpies of Elements
5.5 Variation of Successive Ionization Ethalpies
with Atomic Numbers
5.4 Atomic Size of Elements
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.112)
Relative Energies of Orbitals
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.112)
Building up of Electronic Configurations
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.112)
Aufbau principle states that electrons will enter the
possible orbitals in the order of ascending energy.
Pauli’s exclusion principle states that no two
electrons in the same atom can have identical
values for all four sets of quantum numbers.
Hund’s rule (Rule of maximum multiplicity) states
that electrons must occupy each energy level singly
before pairing takes place (because of their mutual
repulsion) and only then does pairing occur.
Carbon
4
1s
2s
2p
New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.114)
Classwork
Draw the electron-in-box diagrams and write the
electronic configurations for the first 20 elements in
the Periodic Table.
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.114)
Element
Electron-in-box Diagram
Electronic Configuration
1s1
1H
1s
8O
1s22s22p4
1s
2s
2p
11Na
1s22s22p63s2
1s
6
2s
2p
3s
New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.114)
19K
1s
2s
2p
3s
3p
3d
4s
3d
4s
Can be simplified as:
[Ar]
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.114)
Classwork
Draw the electron-in-box diagrams and write the
electronic configurations for the elements with
atomic numbers from 21 to 30.
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New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative Energies of Orbitals (SB p.114)
21Sc
24Cr
[Ar]
3d
4s
3d
4s
[Ar]
Halfly-filled subshell  extra stability
29Cu
[Ar]
3d
4s
Fully-filled subshell  extra stability
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New Way Chemistry for Hong Kong A-Level Book 1
5.2 Relative Electronic Configurations of Elements (p. 114)
Electronic Configurations of Isolated Atoms
Atomic
no.
1
2
3
4
5
6
7
8
10
Element
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Symbol
H
He
Li
Be
B
C
N
O
Arrangement of
electrons in
shells
1
2
2,1
2,2
2,3
2,4
2,5
2,6
Electronic configuration
“Standard
form”
1s1
1s2
1s22s1
1s22s2
1s22s22p1
1s22s22p2
1s22s22p3
1s22s22p4
New Way Chemistry for Hong Kong A-Level Book 1
“Abbreviated
form”
1s1
1s2
[He]2s1
[He]2s2
[He]2s22p1
[He]2s22p2
[He]2s22p3
[He]2s22p4
5.2 Relative Electronic Configurations of Elements (p. 115)
Electronic Configurations of Isolated Atoms
Atomic
no.
9
10
11
12
13
14
15
16
11
Element
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phoshporus
Sulphur
Symbol Arrangement
of electrons
in shells
F
Ne
Na
Mg
Al
Si
P
S
2,7
2,8
2,8,1
2,8,2
2,8,3
2,8,4
2,8,5
2,8,6
Electronic configuration
“Standard form” “Abbreviated
form”
1s22s22p5
1s22s22p6
1s22s22p63s1
1s22s22p63s2
1s22s22p63s23p1
1s22s22p63s23p2
1s22s22p63s23p3
1s22s22p63s23p4
New Way Chemistry for Hong Kong A-Level Book 1
[He]2s22p5
[He]2s22p6
[Ne]3s1
[Ne]3s2
[Ne]3s23p1
[Ne]3s23p2
[Ne]3s23p3
[Ne]3s23p4
5.2 Relative Electronic Configurations of Elements (p. 115)
Electronic Configurations of Isolated Atoms
Atomic
no.
17
18
19
20
12
Element
Chlorine
Argon
Potassium
Calcium
Symbol
Cl
Ar
K
Ca
Arrangement of
electrons
in shells
2,8,7
2,8,8
2,8,8,1
2,8,8,2
Electronic configuration
“Standard form”
1s22s22p63s23p5
1s22s22p63s23p6
1s22s22p63s23p64s1
1s22s22p63s23p64s2
New Way Chemistry for Hong Kong A-Level Book 1
“Abbreviated form”
[Ne]3s23p5
[Ne]3s23p6
[Ar]4s1
Ar]4s2
5.2 Relative Electronic Configurations of Elements (p. 117)
Represented by ‘Electron-in-boxes’ Diagrams
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New Way Chemistry for Hong Kong A-Level Book 1
5.2 Relative Electronic Configurations of Elements (p. 117)
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New Way Chemistry for Hong Kong A-Level Book 1
5.3 The Periodic Table (p. 118)
The Periodic Table
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New Way Chemistry for Hong Kong A-Level Book 1
5.3 The Periodic Table (p. 118)
s-block
p-block
d-block
f-block
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New Way Chemistry for Hong Kong A-Level Book 1
5.3 The Periodic Table (p. 119)
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5.4 Ionization Enthalpies of Elements (p. 120)
Ionization Enthalpies of Elements
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 121)
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 122)
Ionization Enthalpy across a Period
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 122)
Q: Explain why there is a general increase in the
ionization energy across a period.
•Moving across a period, there is an increase in the
nuclear attraction due to the addition of proton in the
nucleus.
•The added electron is placed in the same quantum shell.
It is only poorly shielded by other electrons in that shell.
•The nuclear attraction outweighs the increase in the
shielding effect between the electrons. This leads to an
increase in the effective nuclear charge.
•The increase in the effective nuclear charge causes a
decrease in the atomic radius.
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
Q: Explain why there is a trough at Boron(B) in Period 2.
• e.c. of Be : 1s22s2
e.c. of B : 1s22s22p1
• It is easier to remove the less penetrating pelectron from B than to remove a s electron from a
stable fully-filled 2s subshell in Be.
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
Q: Explain why there is a trough at Oxygen(O) in Period 2.
• e.c. of N : 1s22s22p3
e.c. of O : 1s22s22p4
• It is more difficult to remove an electron from the
halfly-filled 2p subshell of P, which has extra
stability.
• After the removal of a p electron, a stable halffilled 2 p subshell can be obtained for Q.
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
Q: Explain why there is large drop of I.E. between periods.
• The element at the end of a period has a stable
octet structure. Much energy is required to
remove an electron from it as this will disturb the
stable structure.
• The element at the beginning of the next period
has one extra s electron in an outer quantum shell.
Although there is also an increase in the nuclear
charge, it is offset very effectively by the
screening effect of the inner shell electrons.
• Thus the atomic radius increases, making the
nucleus less effective in holding the s electron in
the outer shell
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
Q: Explain why there is drop of I.E. down a group.
• In moving down a group, although there is an
increase in the nuclear charge, it is offset very
effectively by the screening effect of the inner
shell electrons.
• Thus the atomic radius increases, making the
nucleus less effective in holding the s electron in
the outer shell
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
Q: Explain why successive ionization energies increase.
• It is more difficult to remove electron(negatively
charged) from higher positively charged ions.
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization Enthalpies of Elements (p. 123)
Q: Explain why successive ionization energy curve
follows the same pattern as the last one, but is
shifted by one unit of atomic number to the right.
• It is because the electronic configuration of AZ+
is the same as Az-1.
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New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of Successive Ionization Enthalpies with Atomic Numbers (p. 124)
Successive Ionization Enthalpies with Atomic Number
Atomic
number
1
2
3
4
5
6
7
8
9
10
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ΔH I.E. (kJ mol-1)
Element
H
He
Li
Be
B
C
N
O
F
Ne
1 st
2nd
3rd
4th
1 310
2 370
519
900
799
1 090
1 400
1 310
1 680
2 080
5 250
7 300
1 760
2 420
2 350
2 860
3 390
3 370
3 950
11 800
14 800
3 660
4 610
4 509
5 320
6 040
6 150
21 000
25 000
6 220
7 480
7 450
8 410
9 290
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of Successive Ionization Enthalpies with Atomic Numbers (p. 124)
Atomic
number
11
12
13
14
15
16
17
18
19
20
33
ΔH I.E. (kJ mol-1)
Element
Na
Mg
Al
SI
P
S
Cl
Ar
K
Ca
1 st
2nd
3rd
4th
494
736
577
786
1 060
1 000
1 260
1 520
418
590
4 560
1 450
1 820
1 580
1 900
2 260
2 300
2 660
3 070
1 150
6 940
7 740
2 740
3 230
2 920
3 390
3 850
3 950
4 600
4 940
9 540
10 500
11 600
4 360
4 960
4 540
5 150
5 77
5 860
6 480
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of Successive Ionization Enthalpies with Atomic Numbers (p. 126)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
Atomic size of elements
…..
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
Q: Explain why the atomic radius decreases across a period.
• Moving across a period, there is an increase in the
nuclear attraction due to the addition of proton in the
nucleus.
• The added electron is placed in the same quantum
shell.
It is only poorly shielded/screened by other electrons
in that shell.
• The nuclear attraction outweighs the increase in the
shielding effect between the electrons. This leads to an
increase in the effective nuclear charge.
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
+11
Sodium atom Na
(2,8,1)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
+9
Sodium atom Na
(2,8,1)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
+1
Effective nuclear charge = +1
Sodium atom Na
(2,8,1)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
+12
Magnesium Mg
(2,8,2)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
+10
Magnesium Mg
(2,8,2)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 128)
+2
Magnesium Mg
(2,8,2)
By similar argument, effective nuclear charge = +2 for a Mg atom.
Thus effective nuclear charge increases across a period.
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 129)
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 129)
Q: Explain why the atomic radius increases down a group.
• Moving down a group, although there is an
increase in the nuclear charge, it is offset very
effectively by the screening effect of the inner
shell electrons.
• Moving down a group, an atom would have one
more electron shell occupied which lies at a
greater distance from the nucleus.
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New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic Size of Elements (p. 129)
Remarks:
Effective nuclear charge can only be applied to
make comparison between atoms in the same
period.
Never apply effective nuclear charge to atoms in
the same group.
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New Way Chemistry for Hong Kong A-Level Book 1
The END
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New Way Chemistry for Hong Kong A-Level Book 1