Periodic Properties and Chemical Bonding (Theory) IIT JAM Notes | EduRev

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IIT JAM : Periodic Properties and Chemical Bonding (Theory) IIT JAM Notes | EduRev

 Page 1


TOPIC: PerIOdIC PrOPerTIes and
chemical bonding
TargeT csir-neT (june) 2015
2637, Hudson Lane, Behind Khalsa College, Near G.T.B. Nagar Metro Station Gate
No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com,
www.asfinstitute.com
inorganic chemistry
A
S
F
A
S
F
Page 2


TOPIC: PerIOdIC PrOPerTIes and
chemical bonding
TargeT csir-neT (june) 2015
2637, Hudson Lane, Behind Khalsa College, Near G.T.B. Nagar Metro Station Gate
No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com,
www.asfinstitute.com
inorganic chemistry
A
S
F
A
S
F
2
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
Periodic Properties
Periodic Table is the arrangement of the elements in tabular form according to their properties so that similar
elements fall within the same vertical column and dissimilar elements are separated.
Table: Periodic T able
3
Li
1
H
11
Na
19
K
37
Rb
55
Cs
87
Fr
2A
4
Be
12
Mg
20
Ca
38
Sr
56
Ba
88
Ra
89
Rc**
57
La*
39
Y
21
Sc
3B 4B 5B 6B 7B 8B 1B 2B
22
Ti 
40
Zr
72
Hf
104
Rf
23
V 
41
Nb
73
Ta
105
Ha
58
Ce
90
Th
24
Cr
25
Mn
26
Fe
27
Cd
28
Ni 
29
Cu
30
Zn
31
Ga
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
74
W
75
Re
76
Ir
77
It
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
105
Ha
106
Sg
107
Ns
108
Hs
109
Mt
110 111
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cr
98
Cr
99
Es
101
Fm
102
No
103
Lr
32
Ge
33
Rs
34
Se
35
Br
36
Kr
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
1A
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
5
B
6
C
7
N
8
O
9
F
10
Ne
1
H
2
He
3A 4A 5A 6A
7A 8A
Lanthanide*
Series
Actinide**
Series
  MODERN PERIODIC LA W
The properties of elements are periodic functions of their atomic numbers. If elements are arranged in
increasing order of their atomic numbers, there is repetition of properties after 2, 8, 18 and 32 elements.
The numbers 2, 8, 18 and 32 are also referred as magic numbers.
  LONG FORM OF PERIODIC TABLE
The elements have been arranged in the increasing order of atomic number.
The horizontal rows constitute periods while the vertical rows constitute groups or families.
Periodic table is divided into four main blocks. These are s, p, d and f-blocks. The division of elements
into a blocks is primarily based upon their electronic configuration.
Page 3


TOPIC: PerIOdIC PrOPerTIes and
chemical bonding
TargeT csir-neT (june) 2015
2637, Hudson Lane, Behind Khalsa College, Near G.T.B. Nagar Metro Station Gate
No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com,
www.asfinstitute.com
inorganic chemistry
A
S
F
A
S
F
2
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
Periodic Properties
Periodic Table is the arrangement of the elements in tabular form according to their properties so that similar
elements fall within the same vertical column and dissimilar elements are separated.
Table: Periodic T able
3
Li
1
H
11
Na
19
K
37
Rb
55
Cs
87
Fr
2A
4
Be
12
Mg
20
Ca
38
Sr
56
Ba
88
Ra
89
Rc**
57
La*
39
Y
21
Sc
3B 4B 5B 6B 7B 8B 1B 2B
22
Ti 
40
Zr
72
Hf
104
Rf
23
V 
41
Nb
73
Ta
105
Ha
58
Ce
90
Th
24
Cr
25
Mn
26
Fe
27
Cd
28
Ni 
29
Cu
30
Zn
31
Ga
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
74
W
75
Re
76
Ir
77
It
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
105
Ha
106
Sg
107
Ns
108
Hs
109
Mt
110 111
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cr
98
Cr
99
Es
101
Fm
102
No
103
Lr
32
Ge
33
Rs
34
Se
35
Br
36
Kr
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
1A
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
5
B
6
C
7
N
8
O
9
F
10
Ne
1
H
2
He
3A 4A 5A 6A
7A 8A
Lanthanide*
Series
Actinide**
Series
  MODERN PERIODIC LA W
The properties of elements are periodic functions of their atomic numbers. If elements are arranged in
increasing order of their atomic numbers, there is repetition of properties after 2, 8, 18 and 32 elements.
The numbers 2, 8, 18 and 32 are also referred as magic numbers.
  LONG FORM OF PERIODIC TABLE
The elements have been arranged in the increasing order of atomic number.
The horizontal rows constitute periods while the vertical rows constitute groups or families.
Periodic table is divided into four main blocks. These are s, p, d and f-blocks. The division of elements
into a blocks is primarily based upon their electronic configuration.
3
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
s-Block Elements
(Electronic Configuration n s )
n = 1, 2, 3, 4, 5, 6, 7
1–2
IA
IIA
Alkali Metals
Alkaline Earth Metals
d-Block Elements
(transition elements)
Electronic Configuration
(n–1)d ns
n = 3, 4, 5
1–10 1–2
Metals
f-block elements
(Inner transition elements)
(n–2)f (n–1)d ns
1–2 1–10 0–1
Lanthanides and 
Actinide Metals  with
n = 4 and 5 respectively
Noble gases
p-Block Elements
ns np
n = 1, 2, 3, 4, 5, 6, 7
2 1–6
non-metals
Metalloid 
Commonly used terms
(i) Representative elements : All the s and p block elements are known as representative elements
except zero group.
(ii) Typical elements : Elements of second and third period are known as typical elements.
CLASSIFICATION OF ELEMENTS AS METALS, NON-METALS AND METALLOIDS
(1) Metals
About 80% of the elements are metals. Metals are the elements which are malleable and ductile,
possess luster, are good conductors of heat, electricity and have high densities. Metals usually have high
melting and boiling points, and are generally solids at room temperature. “Mercury is the only which
is liquid at room temperature”. Gallium (303 K) also have very low melting points.
(2) Non-Metals
Non-metals are much less in number than metals. Non-metals have low melting and boiling points.
They are usually solids or gases at room temperature. Non-metals are neither malleable nor ductile.
They are poor conductors of heat and electricity. The non-metallic character increases going from left
to right and metallic character increases going down a group.
(3) Metalloids
There is no sharp dividing metals from non-metals. A zig-zag line separates metals from non-metals as
shown in figure. The borderline elements such as silicon, germanium, arsenic, antimony and tellurium
exhibit characteristic properties of metals as well as non-metals. These elements are called semimetals
or metalloids.
  IUPAC NOMENCLATURE FOR ELEMENTS WITH Z > 100
The elements beyond uranium (Z = 92) are all synthetic elements and are known as trans uranium
elements. The elements beyond fermium (Z = 100) are known as trans fermium elements. These
elements have atomic number 101 onwards.
The elements fermium (Z = 100), mendelevium (Z = 101), nobelium (Z = 102) and lawrencium (Z =
103) are named after the names of famous scientists.
Nomenclature of the elements:
The names are derived by using roots for the three digits in the atomic number of the element and
adding the ending –ium. The roots for the number are
Page 4


TOPIC: PerIOdIC PrOPerTIes and
chemical bonding
TargeT csir-neT (june) 2015
2637, Hudson Lane, Behind Khalsa College, Near G.T.B. Nagar Metro Station Gate
No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com,
www.asfinstitute.com
inorganic chemistry
A
S
F
A
S
F
2
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
Periodic Properties
Periodic Table is the arrangement of the elements in tabular form according to their properties so that similar
elements fall within the same vertical column and dissimilar elements are separated.
Table: Periodic T able
3
Li
1
H
11
Na
19
K
37
Rb
55
Cs
87
Fr
2A
4
Be
12
Mg
20
Ca
38
Sr
56
Ba
88
Ra
89
Rc**
57
La*
39
Y
21
Sc
3B 4B 5B 6B 7B 8B 1B 2B
22
Ti 
40
Zr
72
Hf
104
Rf
23
V 
41
Nb
73
Ta
105
Ha
58
Ce
90
Th
24
Cr
25
Mn
26
Fe
27
Cd
28
Ni 
29
Cu
30
Zn
31
Ga
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
74
W
75
Re
76
Ir
77
It
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
105
Ha
106
Sg
107
Ns
108
Hs
109
Mt
110 111
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cr
98
Cr
99
Es
101
Fm
102
No
103
Lr
32
Ge
33
Rs
34
Se
35
Br
36
Kr
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
1A
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
5
B
6
C
7
N
8
O
9
F
10
Ne
1
H
2
He
3A 4A 5A 6A
7A 8A
Lanthanide*
Series
Actinide**
Series
  MODERN PERIODIC LA W
The properties of elements are periodic functions of their atomic numbers. If elements are arranged in
increasing order of their atomic numbers, there is repetition of properties after 2, 8, 18 and 32 elements.
The numbers 2, 8, 18 and 32 are also referred as magic numbers.
  LONG FORM OF PERIODIC TABLE
The elements have been arranged in the increasing order of atomic number.
The horizontal rows constitute periods while the vertical rows constitute groups or families.
Periodic table is divided into four main blocks. These are s, p, d and f-blocks. The division of elements
into a blocks is primarily based upon their electronic configuration.
3
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
s-Block Elements
(Electronic Configuration n s )
n = 1, 2, 3, 4, 5, 6, 7
1–2
IA
IIA
Alkali Metals
Alkaline Earth Metals
d-Block Elements
(transition elements)
Electronic Configuration
(n–1)d ns
n = 3, 4, 5
1–10 1–2
Metals
f-block elements
(Inner transition elements)
(n–2)f (n–1)d ns
1–2 1–10 0–1
Lanthanides and 
Actinide Metals  with
n = 4 and 5 respectively
Noble gases
p-Block Elements
ns np
n = 1, 2, 3, 4, 5, 6, 7
2 1–6
non-metals
Metalloid 
Commonly used terms
(i) Representative elements : All the s and p block elements are known as representative elements
except zero group.
(ii) Typical elements : Elements of second and third period are known as typical elements.
CLASSIFICATION OF ELEMENTS AS METALS, NON-METALS AND METALLOIDS
(1) Metals
About 80% of the elements are metals. Metals are the elements which are malleable and ductile,
possess luster, are good conductors of heat, electricity and have high densities. Metals usually have high
melting and boiling points, and are generally solids at room temperature. “Mercury is the only which
is liquid at room temperature”. Gallium (303 K) also have very low melting points.
(2) Non-Metals
Non-metals are much less in number than metals. Non-metals have low melting and boiling points.
They are usually solids or gases at room temperature. Non-metals are neither malleable nor ductile.
They are poor conductors of heat and electricity. The non-metallic character increases going from left
to right and metallic character increases going down a group.
(3) Metalloids
There is no sharp dividing metals from non-metals. A zig-zag line separates metals from non-metals as
shown in figure. The borderline elements such as silicon, germanium, arsenic, antimony and tellurium
exhibit characteristic properties of metals as well as non-metals. These elements are called semimetals
or metalloids.
  IUPAC NOMENCLATURE FOR ELEMENTS WITH Z > 100
The elements beyond uranium (Z = 92) are all synthetic elements and are known as trans uranium
elements. The elements beyond fermium (Z = 100) are known as trans fermium elements. These
elements have atomic number 101 onwards.
The elements fermium (Z = 100), mendelevium (Z = 101), nobelium (Z = 102) and lawrencium (Z =
103) are named after the names of famous scientists.
Nomenclature of the elements:
The names are derived by using roots for the three digits in the atomic number of the element and
adding the ending –ium. The roots for the number are
4
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
Digit Name Abbreviation
0 nil n
1 un u
2 bi b
3 tri t
4 quad q
5 pent p
6 hex h
7 sept s
8 oct o
9 enn e
Thus element with atomic number 109 will be named as une (u for 1, n for 0 and e for 9). Table
summarises the names of the elements with atomic number above 100.
  EFFECTIVE NUCLEAR CHARGE (Z*)
• It is the nuclear attractive force experienced by the e
-
 when it is shielded by inner lying electrons.
• 2p e
–
 is shielded more than or 2s e
–
 as it penetrates the 1s orbital less than 2s orbital.
• As a result we have the energy sequence:  [2s < 2p],   [3s < 3p < 3d] and  [4s < 4p < 4d < 4f]
• As we move to atoms of elements of higher atomic number, the energy difference between orbitals of
same value of n decreases.
Screening Effect:
• The e
?
s of inner shell repel the e
?
s of outer most shells. This effect is known as screening or shielding
effect.
• The e
?
s of outer most shell are thus shielded or screened from the nucleus by inner e
?
s.
• As a result of screening effect the outer most e
-
s do not experience the complete nuclear charge.
• So an increase in no. of inner e
-
s increases screening effect and an increase in screening effect decreases
Nuclear charge. This results in decrease of I.E.
Nature of orbitals containing e
–
s : (Penetrating effect of e
?
s)
• The penetrating power of e
-
s towards the nucleus in a given shell decreases in the order s > p > d > f.
• If penetration of e- is more, it will be more tightly held up by the nucleus, so it will be difficul t to remove
it.
• That means the I.E. increases with increase in penetrating power of e
–
s in the subshells.
Empirical Rules for estimating ENC -  “Slater Rule”
• The actual nuclear charge experienced by the electrons in different orbitals is estimated by Slater
Rules.
• The ENC (Z*) acting on a given e
-
 is obtained by subtracting the screening (shielding) constant ‘S’.
Z*(ENC) = Z(Nuclear charge) – S(Shielding constant)
(i) Write the electronic configuration in the following order and groupings
(1s), (2s, 2p), (3s, 3p)(3d), (4s, 4p), (4d) (4f), (5s, 5p) etc.
(ii) Electron in any group higher in this sequence than the electron under consideration contribute
nothing to ‘S’.
Page 5


TOPIC: PerIOdIC PrOPerTIes and
chemical bonding
TargeT csir-neT (june) 2015
2637, Hudson Lane, Behind Khalsa College, Near G.T.B. Nagar Metro Station Gate
No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com,
www.asfinstitute.com
inorganic chemistry
A
S
F
A
S
F
2
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
Periodic Properties
Periodic Table is the arrangement of the elements in tabular form according to their properties so that similar
elements fall within the same vertical column and dissimilar elements are separated.
Table: Periodic T able
3
Li
1
H
11
Na
19
K
37
Rb
55
Cs
87
Fr
2A
4
Be
12
Mg
20
Ca
38
Sr
56
Ba
88
Ra
89
Rc**
57
La*
39
Y
21
Sc
3B 4B 5B 6B 7B 8B 1B 2B
22
Ti 
40
Zr
72
Hf
104
Rf
23
V 
41
Nb
73
Ta
105
Ha
58
Ce
90
Th
24
Cr
25
Mn
26
Fe
27
Cd
28
Ni 
29
Cu
30
Zn
31
Ga
42
Mo
43
Tc
44
Ru
45
Rh
46
Pd
47
Ag
48
Cd
49
In
50
Sn
51
Sb
52
Te
53
I
54
Xe
74
W
75
Re
76
Ir
77
It
78
Pt
79
Au
80
Hg
81
Tl
82
Pb
83
Bi
84
Po
85
At
86
Rn
105
Ha
106
Sg
107
Ns
108
Hs
109
Mt
110 111
59
Pr
60
Nd
61
Pm
62
Sm
63
Eu
64
Gd
65
Tb
66
Dy
91
Pa
92
U
93
Np
94
Pu
95
Am
96
Cm
97
Bk
98
Cr
98
Cr
99
Es
101
Fm
102
No
103
Lr
32
Ge
33
Rs
34
Se
35
Br
36
Kr
67
Ho
68
Er
69
Tm
70
Yb
71
Lu
1A
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
5
B
6
C
7
N
8
O
9
F
10
Ne
1
H
2
He
3A 4A 5A 6A
7A 8A
Lanthanide*
Series
Actinide**
Series
  MODERN PERIODIC LA W
The properties of elements are periodic functions of their atomic numbers. If elements are arranged in
increasing order of their atomic numbers, there is repetition of properties after 2, 8, 18 and 32 elements.
The numbers 2, 8, 18 and 32 are also referred as magic numbers.
  LONG FORM OF PERIODIC TABLE
The elements have been arranged in the increasing order of atomic number.
The horizontal rows constitute periods while the vertical rows constitute groups or families.
Periodic table is divided into four main blocks. These are s, p, d and f-blocks. The division of elements
into a blocks is primarily based upon their electronic configuration.
3
2637, Hudson Lane, Behind Khalsa College, Near G .T.B. Nagar Metro Station Gate No. 3 & 4, New Delhi - 110009
Mob. 09555785548, 08860929430, e-mail: info@asfinstitute.com, www .asfinstitute.com
PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
s-Block Elements
(Electronic Configuration n s )
n = 1, 2, 3, 4, 5, 6, 7
1–2
IA
IIA
Alkali Metals
Alkaline Earth Metals
d-Block Elements
(transition elements)
Electronic Configuration
(n–1)d ns
n = 3, 4, 5
1–10 1–2
Metals
f-block elements
(Inner transition elements)
(n–2)f (n–1)d ns
1–2 1–10 0–1
Lanthanides and 
Actinide Metals  with
n = 4 and 5 respectively
Noble gases
p-Block Elements
ns np
n = 1, 2, 3, 4, 5, 6, 7
2 1–6
non-metals
Metalloid 
Commonly used terms
(i) Representative elements : All the s and p block elements are known as representative elements
except zero group.
(ii) Typical elements : Elements of second and third period are known as typical elements.
CLASSIFICATION OF ELEMENTS AS METALS, NON-METALS AND METALLOIDS
(1) Metals
About 80% of the elements are metals. Metals are the elements which are malleable and ductile,
possess luster, are good conductors of heat, electricity and have high densities. Metals usually have high
melting and boiling points, and are generally solids at room temperature. “Mercury is the only which
is liquid at room temperature”. Gallium (303 K) also have very low melting points.
(2) Non-Metals
Non-metals are much less in number than metals. Non-metals have low melting and boiling points.
They are usually solids or gases at room temperature. Non-metals are neither malleable nor ductile.
They are poor conductors of heat and electricity. The non-metallic character increases going from left
to right and metallic character increases going down a group.
(3) Metalloids
There is no sharp dividing metals from non-metals. A zig-zag line separates metals from non-metals as
shown in figure. The borderline elements such as silicon, germanium, arsenic, antimony and tellurium
exhibit characteristic properties of metals as well as non-metals. These elements are called semimetals
or metalloids.
  IUPAC NOMENCLATURE FOR ELEMENTS WITH Z > 100
The elements beyond uranium (Z = 92) are all synthetic elements and are known as trans uranium
elements. The elements beyond fermium (Z = 100) are known as trans fermium elements. These
elements have atomic number 101 onwards.
The elements fermium (Z = 100), mendelevium (Z = 101), nobelium (Z = 102) and lawrencium (Z =
103) are named after the names of famous scientists.
Nomenclature of the elements:
The names are derived by using roots for the three digits in the atomic number of the element and
adding the ending –ium. The roots for the number are
4
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PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
Digit Name Abbreviation
0 nil n
1 un u
2 bi b
3 tri t
4 quad q
5 pent p
6 hex h
7 sept s
8 oct o
9 enn e
Thus element with atomic number 109 will be named as une (u for 1, n for 0 and e for 9). Table
summarises the names of the elements with atomic number above 100.
  EFFECTIVE NUCLEAR CHARGE (Z*)
• It is the nuclear attractive force experienced by the e
-
 when it is shielded by inner lying electrons.
• 2p e
–
 is shielded more than or 2s e
–
 as it penetrates the 1s orbital less than 2s orbital.
• As a result we have the energy sequence:  [2s < 2p],   [3s < 3p < 3d] and  [4s < 4p < 4d < 4f]
• As we move to atoms of elements of higher atomic number, the energy difference between orbitals of
same value of n decreases.
Screening Effect:
• The e
?
s of inner shell repel the e
?
s of outer most shells. This effect is known as screening or shielding
effect.
• The e
?
s of outer most shell are thus shielded or screened from the nucleus by inner e
?
s.
• As a result of screening effect the outer most e
-
s do not experience the complete nuclear charge.
• So an increase in no. of inner e
-
s increases screening effect and an increase in screening effect decreases
Nuclear charge. This results in decrease of I.E.
Nature of orbitals containing e
–
s : (Penetrating effect of e
?
s)
• The penetrating power of e
-
s towards the nucleus in a given shell decreases in the order s > p > d > f.
• If penetration of e- is more, it will be more tightly held up by the nucleus, so it will be difficul t to remove
it.
• That means the I.E. increases with increase in penetrating power of e
–
s in the subshells.
Empirical Rules for estimating ENC -  “Slater Rule”
• The actual nuclear charge experienced by the electrons in different orbitals is estimated by Slater
Rules.
• The ENC (Z*) acting on a given e
-
 is obtained by subtracting the screening (shielding) constant ‘S’.
Z*(ENC) = Z(Nuclear charge) – S(Shielding constant)
(i) Write the electronic configuration in the following order and groupings
(1s), (2s, 2p), (3s, 3p)(3d), (4s, 4p), (4d) (4f), (5s, 5p) etc.
(ii) Electron in any group higher in this sequence than the electron under consideration contribute
nothing to ‘S’.
5
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PERIODIC PROPERTIES & CHEMICAL BONDING ASHOKA SCIENTIFIC FORUM
(iii) Then for an e
–
 in an ‘ns’ or np orbital.
(a) All other electrons in the (ns, np) group contribute S = 0.35 each.
(b) All electrons in the (n – 1) shell contribute S = 0.85 each.
(c) All electrons in (n – 2) or lower shells contribute S = 1.00 each.
(4) For an electron in nd or nf orbital, all electrons in the same group contribute s = 0.35 each.
• Those in groups lying lower in the sequence than (nd) or (nf) contribute s = 1.00 each.
Example: ‘K’ = (1s
2
)(2s
2
p
6
)(3s
2
p
6
)(4s
1
).
The ENC experienced by ‘4s’ e
?
 is  Z* = Z – S = 19 – (0.85 × 8) + (1.00 × 10) = 2.20
? If we consider the E.C. of K as (1s
2
)(2s
2
p
6
)(3s
2
p
6
)(3d
1
) then Z* would be Z* = 19 – (1 × 18) = 1
? Thus the e
–
 in the 4s orbital is under the influence of the greater effective nuclear charge and hence
in the ground state it is this orbital that is occupied.
  PERIODICITY IN PROPERTIES
The periodicity is repetition of elements with similar properties after certain regular intervals when the
elements are arranged in order of increasing atomic number.
The periodic repetition of properties is due to the recurrence of similar valence shell configurations after
regular intervals.
Atomic Size
Factors affecting atomic size
(a) n increase size increases (n = principal of quantum number)
(b) Z
eff
 increase, size decrease [Z
eff
 = Z – ?]
Periodic Trends
In a period (L ? R) :  Atomic size decreases from left to right in a period.
Looking to the E.C. of elements, following observations are made,
• The e
-
s enter in the same shell,
• The no. of protons are increasing from left to right with increase in atomic no.
• The nuclear charge is increasing, so the attractive force of nucleus on outermost e
–
 is increasing.
This results in net contraction of atomic size.
In a group (up to down): Atomic size increases from top to down in a group.
The electronic configuration of elements of the same group indicates that e
-
s are added in the new
shell in the senior atom. i.e. a new shell is added in the next higher group.
• Although no. of protons are also increasing (i.e. increase in nuclear charge) but the net result is
increase in size of the atom.
The net attractive force of nucleus decreases down the group.
Atomic Radii
An atom does not have any sharp boundary,
• So the atomic radius is determined by indirect method in the combined state of an atom.
The atomic radii of atoms of compounds are classified as :
Read More
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