Download 5.4

5
5.1
5.2
Relative Energies of Orbitals
Electronic Configurations of Elements
5.3
5.4
5.5
The Periodic Table
Ionization Enthalpies of Elements
Variation of Successive Ionization Ethalpies
with Atomic Numbers
Atomic Size of Elements
5.4
1
Electronic Configurations
and the Periodic Table
New Way Chemistry for Hong Kong A-Level Book 1
5.1
Relative Energies
of Orbitals
2
New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative energies of orbitals (SB p.106)
Relative energies of orbitals
3
New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative energies of orbitals (SB p.106)
Building up of electronic configurations
4
New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative energies of orbitals (SB p.106)
Aufbau principle states that electrons will enter the
possible orbitals in the order of ascending energy.
Pauli’s exclusion principle states that electrons
occupying the same orbital must have opposite spins.
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).
Carbon
1s
5
2s
2p
Check Point 5-1
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5.2
Electronic
Configurations of
Elements
6
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5.2 Electronic configurations of elements (SB p.108)
Represented by notations
Atomic Element
no.
1
2
3
4
5
6
7
8
7
Hydrogen
Helium
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Symbol
H
He
Li
Be
B
C
N
O
Arrangement
Electronic configuration
of electrons in “Standard “Abbreviated
shells
form”
form”
1
1s1
1s1
2
1s2
1s2
2, 1
1s22s1
[He]2s1
2, 2
1s22s2
[He]2s2
2, 3
1s22s22p1 [He]2s22p1
2, 4
1s22s22p2 [He]2s22p2
2, 5
1s22s22p3 [He]2s22p3
2, 6
1s22s22p4 [He]2s22p4
New Way Chemistry for Hong Kong A-Level Book 1
5.2 Electronic configurations of elements (SB p.109)
Represented by notations
Atomic
no.
Element
9
10
11
12
13
14
15
16
Fluorine
Neon
Sodium
Magnesium
Aluminium
Silicon
Phoshporus
Sulphur
8
Symbol Arrangeme
Electronic configuration
nt of
electrons
in shells “Standard form” “Abbreviat
ed form”
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
1s22s22p5
1s22s22p6
1s22s22p63s1
1s22s22p63s2
1s22s22p63s23p1
1s22s22p63s23p2
1s22s22p63s23p3
1s22s22p63s23p4
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[He]2s22p5
[He]2s22p6
[Ne]3s1
[Ne]3s2
[Ne]3s23p1
[Ne]3s23p2
[Ne]3s23p3
[Ne]3s23p4
5.2 Electronic configurations of elements (SB p.109)
Represented by notations
Atomic
no.
17
18
19
20
9
Element
Symbol Arrange
-ment of
electron
s in
shells
Chlorine
Cl
2,8,7
Argon
Ar
2,8,8
Potassium K
2,8,8,1
Calcium
Ca
2,8,8,2
Electronic configuration
“Standard form”
1s22s22p63s23p5
1s22s22p63s23p6
1s22s22p63s23p64s1
1s22s22p63s23p64s2
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“Abbreviated form”
[Ne]3s23p5
[Ne]3s23p6
[Ar]4s1
[Ar]4s2
5.2 Electronic configurations of elements (SB p.110)
Represented by ‘electrons-in-boxes’ diagrams
10
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5.2 Electronic configurations of elements (SB p.110)
11
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Check Point 5-2
5.3
12
The Periodic
Table
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5.3 The Periodic Table (SB p.112)
The Periodic Table
13
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5.3 The Periodic Table (SB p.112)
s-block
p-block
d-block
f-block
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5.3 The Periodic Table (SB p.112)
Check Point 5-3
15
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5.4
Ionization Enthalpies
of Elements
16
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5.4 Ionization enthalpies of elements (SB p.115)
Ionization enthalpies of elements
17
The first
ionization
enthalpies
of the
first 36
elements
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5.4 Ionization enthalpies of elements (SB p.116)
The first
ionization
enthalpies
generally
decrease down
a group and
increases
across a
period
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5.4 Ionization enthalpies of elements (SB p.116)
Ionization enthalpy across a period
19
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5.4 Ionization enthalpies of elements (SB p.116)
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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5.4 Ionization enthalpies of elements (SB p.117)
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New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.117)
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 (SB p.117)
23
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.117)
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.
24
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.117)
25
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.117)
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
26
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.117)
27
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.117)
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 (SB p.117)
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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5.4 Ionization enthalpies of elements (SB p.117)
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.
Check Point 5-4
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New Way Chemistry for Hong Kong A-Level Book 1
5.5
Variation of Successive
Ionization Enthalpies
with Atomic Numbers
31
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 119)
Successive Ionization Enthalpies of the
first 20 elements
Atomic
number
1
2
3
4
5
6
7
8
9
10
32
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. 119)
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
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5.5 Variation of successive ionization enthalpies with atomic numbers (p. 120)
Example 5-5
Check Point 5-5
Variation of the
first, second
and third
ionization
enthalpies of
the first 20
elements
34
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5.6
Atomic Size of
Elements
35
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
Atomic size of elements
…..
36
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
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.
37
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5.6 Atomic size of elements (p. 122)
+11
Sodium atom Na
(2,8,1)
38
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
+9
Sodium atom Na
(2,8,1)
39
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
+1
Effective nuclear
charge = +1
Sodium atom Na
(2,8,1)
40
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
+12
Magnesium atom Mg
(2,8,2)
41
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
+10
Magnesium atom Mg
(2,8,2)
42
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
By similar argument,
effective nuclear
charge = +2 for a Mg
atom.
+2
Magnesium atom Mg
(2,8,2)
Thus effective nuclear charge increases
across a period.
43
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
44
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
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.
45
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 122)
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.
Check Point 5-6
46
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The END
47
New Way Chemistry for Hong Kong A-Level Book 1
5.1 Relative energies of orbitals (SB p.108)
Back
Write the electronic configurations and draw “electrons-in –
boxes” diagrams for
(a) nitrogen; and
(b) sodium.
(a) Nitrogen: 1s22s22p3
(b) Sodium: 1s22s22p63s1
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New Way Chemistry for Hong Kong A-Level Book 1
Answer
5.2 Electronic configurations of elements (SB p.110)
Back
Give the electronic configuration by notations and
“electrons-in-boxes” diagrams in the abbreviated form for
the following elements.
Answer
(a) silicon; and
(b) copper.
(a) Silicon: [Ne]3s23p3
(b) Copper: [Ar]3d104s1
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New Way Chemistry for Hong Kong A-Level Book 1
5.3 The Periodic Table (SB p.113)
Back
If you look at the Periodic Table in Fig. 5-5 closely, you
will find that hydrogen is separated from the rest of the
elements. Even though it has only one electron in its
outermost shell, it cannot be called an alkali metal, why?
Answer
Hydrogen has one electron shell only, with n =1. This shell can
hold a maximum of two electrons. Hydrogen is the only element
with core electrons. This gives it some unusual properties.
Hydrogen can lose one electron to form H+, or gain an electron
to become H-. Therefore, it does not belong to the alkali metals
and halogens. Hydrogen is usually assigned in the space above
the rest of the elements in the Periodic Table – the element
without a family.
50
New Way Chemistry for Hong Kong A-Level Book 1
5.3 The Periodic Table (SB p.114)
Outline the modern Periodic Table and label the table with
the following terms: representative elements, d-transition
elements, f-transition elements, lanthanide series, actinide
series, alkali metals, alkaline earth metals, halogens and
noble gases.
Answer
51
New Way Chemistry for Hong Kong A-Level Book 1
5.3 The Periodic Table (SB p.114)
Back
52
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.118)
(a) Give four main factors that affect the magnitude of
ionization enthalpy of an atom.
Answer
(a) The four main factors that affect the magnitude of the
ionization enthalpy of an atom are:
(1) the electronic configuration of the atom;
(2) the nuclear charge;
(3) the screening effect; and
(4) the atomic radius.
53
New Way Chemistry for Hong Kong A-Level Book 1
5.4 Ionization enthalpies of elements (SB p.118)
(b) Explain why Group 0 elements have extra high first
ionization enthalpies and their decreasing trend down the
group.
(b) The first ionization enthalpies of Group 0 elements are extra high. It is
Answer
because Group 0 elements have very stable electronic configurations
since their orbitals are completely filled. That means, a large amount of
energy is required to remove an electron from a completely filled electron
shell of [ ]ns2np6 configuration.
Going down the group, the first ionization enthalpies of Group 0 elements
decreases. It is because there is an increase in atomic radius down the
group, the outermost shell electrons experience less attraction from the
nucleus. Further, as there is an increase in the number of inner electron
shells, the outermost shell electrons of the atoms are better shielded
from the attraction of the nucleus (greater screening effect).
Consequently, though the nuclear charge increases down the group, the
outermost shell electrons would experience less attraction from the
54 positively charged nucleus. That is why the first ionization enthalpies
New Way Chemistry for Hong Kong A-Level Book 1
decrease down the
group.
5.4 Ionization enthalpies of elements (SB p.118)
Back
(c) Predict the trend of the first ionization enthalpies of the
transition elements.
Answer
(c) The first ionization enthalpies of the transition elements do
not show much variation. The reason is that the first
electron of these atoms to be removed is in the 4s orbital.
As the energy levels of the 4s orbitals of these atoms are
more or less the same, the amount of energy required to
remove these electrons are similar.
55
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 121)
For the element 126C,
(a) (i) write its electronic configuration by notation.
(ii) write its electronic configuration by “electrons-inboxes” diagram.
(a) (i) 1s22s22p2
(ii)
56
New Way Chemistry for Hong Kong A-Level Book 1
Answer
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 121)
(b) The table below gives the successive ionization
enthalpies of carbon.
I.E. (kJ
mol-1)
1st
1090
2nd
2350
3rd
4610
4th
6220
5th
37800
6th
47000
(i) Plot a graph of log [ionization enthalpy] against
number of electrons removed.
(ii) Explain the graph obtained.
57
New Way Chemistry for Hong Kong A-Level Book 1
Answer
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 121)
(b) (i)
58
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 121)
Back
(ii)
59
The ionization enthalpy increases with increasing number of
electrons removed. It is because the effective nuclear charge
increases after an electron is removed, and more energy is
required to remove an electron from a positively charged ion.
Besides, there is a sudden rise from the fourth to the fifth
ionization enthalpy. This is because the fifth ionization enthalpy
involves the removal of an electron from a completely filled 1s
orbital which is very stable.
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 122)
(a) Give the “electrons-in-boxes” diagram of 26Fe.
(a) Fe :
(b) Fe2+ and Fe3+ have 2 and 3 electrons less than Fe
respectively. If the electrons are removed from the 4s
orbital and then 3d orbitals, give the electronic
configurations of Fe2+ and Fe3+.
(b) Fe2+ :
Fe3+ :
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New Way Chemistry for Hong Kong A-Level Book 1
Answer
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 122)
(c) Which ion is more stable, Fe2+ or Fe3+? Explain briefly.
(c) Fe3+ ion is more stable because the 3d orbital is exactly half-filled
which gives the electronic configuration extra stability.
Answer
61
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 122)
(d) Given the successive ionization enthalpies of Fe:
I.E. (kJ
mol-1)
1st
762
2nd
1560
3rd
2960
4th
5400
5th
7620
6th
10100
(i) plot a graph of successive ionization enthalpies in
logarithm scale against the number of electrons
removed;
(ii) state the difference of the plot from that of carbon as
shown in P. 121.
62
New Way Chemistry for Hong Kong A-Level Book 1
Answer
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 122)
(d) (i)
63
Number
of
electrons
removed
1
2
3
4
5
6
log (I.E.)
2.88
3.19
3.47
3.73
3.88
4.00
New Way Chemistry for Hong Kong A-Level Book 1
5.5 Variation of successive ionization enthalpies with atomic numbers (p. 122)
(ii) The ionization enthalpy increases with increasing number of
electrons removed. This is because it requires more energy to
remove an electron from a higher positively charged ion. In
other words, higher successive ionization enthalpies will have
higher magnitudes.
However, the sudden increase from the fourth to the fifth
ionization enthalpies occurs in carbon but not in iron. This
indicates that when electrons are removed from the 4s and 4d
orbitals, there is no disruption of a completely filled electron
shell. Hence, there are no irregularities for the first six
successive ionization enthalpies of iron.
Back
64
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 123)
Explain the following:
(a) The atomic radius decreases across the period from Li to
Ne.
Answer
(a) When moving across the period from Li to Ne, the atomic sizes
progressively decrease with increasing atomic numbers. This is
because an increase in atomic number by one means one more
electron and one more proton in atoms. The additional electron
would cause an increase in repulsion between the electrons in the
outermost shell. However, since each additional electron goes to
the same quantum shell and is at approximately the same distance
from the nucleus, the repulsion between electrons is relatively
ineffective to cause an increase in the atomic radius. On the other
hand, as there is an additional proton added to the nucleus, the
electrons will experience a greater attractive force from the nucleus
(increased effective nuclear charge). Hence, the atomic radii of
atoms decrease across the period from Li to Ne.
65
New Way Chemistry for Hong Kong A-Level Book 1
5.6 Atomic size of elements (p. 123)
Back
Explain the following:
(b) The atomic radius increases down Group I metals.
Answer
(b) Moving down Group I metals, the atoms have more electron shells
occupied. The outermost electron shells become further away from
the nucleus. Besides, the inner shell electrons will shield the outer
shell electrons more effectively from the nuclear charge. This
results in a decrease in the attractive force between the nucleus
and the outer shell electrons. Therefore, the atomic radii of Group I
atoms increase down the group.
66
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