Important Chemical Bonding & Molecular Structure Formulas for JEE and NEET

 Page 1


  
CHEMICAL BONDING
Chemical Bond :
 In the process each atom attains a stable outer electronic configuration
of inert gases.
Ionic or Electrovalent Bond :
The formation of an ionic compound would primarily depends upon :
* The ease of formation of the positive and negative ions from the respective
neutral atoms.
* The arrangement of the positive and negative ions in the solid, that is the
lattice of the crystalline compound.
Conditions for the formation of ionic compounds :
(i) Electronegativity difference between two combining elements must be
larger.
(ii) Ionization enthalpy (M(g) ? M
+
(g) + e
?
) of electropositive element must be
low.
(iii) Negative value of electron gain enthalpy (X (g) + e
?
 ? X
?
(g)) of
electronegative element should be high.
(iv) Lattice enthalpy (M
+
(g) + X
?
 (g) ? MX (s)) of an ionic solid must be high.
Lattice Enthalpy :
The lattice enthalpy of an ionic solid is defined as the energy required to
completely separate one mole of a
solid ionic compound into gaseous constituent ions.
Factors affecting  lattice energy of an ionic compound :
(i) Lattice energy  ? 
1
r r
? ?
?
 where (r
+
 + r?
?
 
) = Inter-ionic Distance.
(ii) Lattice energy  ? Z
+
, Z
?
Z
+
 ? charge on cation in terms electronic
 
charge.
Z
?
 ? charge on anion in terms electronic
 
charge.
Determination of lattice energy :
Born-Haber Cycle :
It inter relates the various energy terms involved during formation of an
ionic compound.
It a thermochemical cycle based on the Hess?s law of constant heat
summation.
Page 2


  
CHEMICAL BONDING
Chemical Bond :
 In the process each atom attains a stable outer electronic configuration
of inert gases.
Ionic or Electrovalent Bond :
The formation of an ionic compound would primarily depends upon :
* The ease of formation of the positive and negative ions from the respective
neutral atoms.
* The arrangement of the positive and negative ions in the solid, that is the
lattice of the crystalline compound.
Conditions for the formation of ionic compounds :
(i) Electronegativity difference between two combining elements must be
larger.
(ii) Ionization enthalpy (M(g) ? M
+
(g) + e
?
) of electropositive element must be
low.
(iii) Negative value of electron gain enthalpy (X (g) + e
?
 ? X
?
(g)) of
electronegative element should be high.
(iv) Lattice enthalpy (M
+
(g) + X
?
 (g) ? MX (s)) of an ionic solid must be high.
Lattice Enthalpy :
The lattice enthalpy of an ionic solid is defined as the energy required to
completely separate one mole of a
solid ionic compound into gaseous constituent ions.
Factors affecting  lattice energy of an ionic compound :
(i) Lattice energy  ? 
1
r r
? ?
?
 where (r
+
 + r?
?
 
) = Inter-ionic Distance.
(ii) Lattice energy  ? Z
+
, Z
?
Z
+
 ? charge on cation in terms electronic
 
charge.
Z
?
 ? charge on anion in terms electronic
 
charge.
Determination of lattice energy :
Born-Haber Cycle :
It inter relates the various energy terms involved during formation of an
ionic compound.
It a thermochemical cycle based on the Hess?s law of constant heat
summation.
  
Hydration :
All the simple salts dissolve in water, producing ions, and consequently
the solution conduct electricity. Since Li
+
  is very small, it is heavily
hydrated. This makes  radius of hydrated Li
+
  ion   large and hence it
moves only slowly. In contrast, Cs
+
   is the least hydrated because of its
bigger size and thus the radius of the Cs
+
  ion is smaller than the radius of
hydrated Li
+
,  and hence hydrated Cs
+
  moves faster, and conducts
electricity more readily.
Hydrolysis :
Hydrolysis means reaction with water molecules ultimately leading to
breaking of O-H bond into H
+
 and OH
?
 ions.
Hydrolysis in covalent compounds takes place generally by two
mechanisms
(a) By Coordinate bond formation : Generally in halides of atoms having
vacant d-orbitals or of halides of atoms having vacant orbitals.
(b) By H-bond formation : For example in Nitrogen trihalides
General properties of ionic compounds :
(a) Physical state : At room temperature ionic compounds exist either in
solid state or in solution phase but not in gaseous state.
(b) Simple ionic compounds do not show isomerism but isomorphism is their
important characteristic.
e.g. ,  FeSO
4
 .7H
2
O | MgSO
4
 . 7H
2
O
(c) Electrical conductivity :
All ionic solids are good conductors in molten state as well as in their
aqueous solutions because their ions are free to move.
(d) Solubility of ionic compounds :
Soluble in polar solvents like water which have high dielectric constant
Covalent character in ionic compounds (Fajan?s rule) :
Fajan?s pointed out that greater is the polarization of anion in a molecule,
more is covalent character in it.
More distortion of anion, more will be polarisation then covalent
character increases.
Page 3


  
CHEMICAL BONDING
Chemical Bond :
 In the process each atom attains a stable outer electronic configuration
of inert gases.
Ionic or Electrovalent Bond :
The formation of an ionic compound would primarily depends upon :
* The ease of formation of the positive and negative ions from the respective
neutral atoms.
* The arrangement of the positive and negative ions in the solid, that is the
lattice of the crystalline compound.
Conditions for the formation of ionic compounds :
(i) Electronegativity difference between two combining elements must be
larger.
(ii) Ionization enthalpy (M(g) ? M
+
(g) + e
?
) of electropositive element must be
low.
(iii) Negative value of electron gain enthalpy (X (g) + e
?
 ? X
?
(g)) of
electronegative element should be high.
(iv) Lattice enthalpy (M
+
(g) + X
?
 (g) ? MX (s)) of an ionic solid must be high.
Lattice Enthalpy :
The lattice enthalpy of an ionic solid is defined as the energy required to
completely separate one mole of a
solid ionic compound into gaseous constituent ions.
Factors affecting  lattice energy of an ionic compound :
(i) Lattice energy  ? 
1
r r
? ?
?
 where (r
+
 + r?
?
 
) = Inter-ionic Distance.
(ii) Lattice energy  ? Z
+
, Z
?
Z
+
 ? charge on cation in terms electronic
 
charge.
Z
?
 ? charge on anion in terms electronic
 
charge.
Determination of lattice energy :
Born-Haber Cycle :
It inter relates the various energy terms involved during formation of an
ionic compound.
It a thermochemical cycle based on the Hess?s law of constant heat
summation.
  
Hydration :
All the simple salts dissolve in water, producing ions, and consequently
the solution conduct electricity. Since Li
+
  is very small, it is heavily
hydrated. This makes  radius of hydrated Li
+
  ion   large and hence it
moves only slowly. In contrast, Cs
+
   is the least hydrated because of its
bigger size and thus the radius of the Cs
+
  ion is smaller than the radius of
hydrated Li
+
,  and hence hydrated Cs
+
  moves faster, and conducts
electricity more readily.
Hydrolysis :
Hydrolysis means reaction with water molecules ultimately leading to
breaking of O-H bond into H
+
 and OH
?
 ions.
Hydrolysis in covalent compounds takes place generally by two
mechanisms
(a) By Coordinate bond formation : Generally in halides of atoms having
vacant d-orbitals or of halides of atoms having vacant orbitals.
(b) By H-bond formation : For example in Nitrogen trihalides
General properties of ionic compounds :
(a) Physical state : At room temperature ionic compounds exist either in
solid state or in solution phase but not in gaseous state.
(b) Simple ionic compounds do not show isomerism but isomorphism is their
important characteristic.
e.g. ,  FeSO
4
 .7H
2
O | MgSO
4
 . 7H
2
O
(c) Electrical conductivity :
All ionic solids are good conductors in molten state as well as in their
aqueous solutions because their ions are free to move.
(d) Solubility of ionic compounds :
Soluble in polar solvents like water which have high dielectric constant
Covalent character in ionic compounds (Fajan?s rule) :
Fajan?s pointed out that greater is the polarization of anion in a molecule,
more is covalent character in it.
More distortion of anion, more will be polarisation then covalent
character increases.
  
Fajan?s gives some rules which govern the covalent character in the ionic
compounds, which are as follows:
(i) Size of cation : Size of cation ? 1 / polarisation.
(ii) Size of anion : Size of anion ? polarisation
(iii) Charge on cation : Charge on cation ? polarisation.
(iv) Charge on anion :  Charge on anion ? polarisation.
(v) Pseudo inert gas configuration of cation :
Covalent Bond :
It forms by sharing of valence electrons between atoms to form molecules
e.g., formation of Cl
2
 molecule :
Cl Cl
Cl Cl
+
8e
?
8e
?
or Cl ? Cl
Covalent bond between two Cl atoms
The important conditions being that :
(i) Each bond Is formed as a result of sharing of an electron pair between the
atoms.
(ii) Each combining atom contributes at least one electron to the shared pair.
(iii) The combining atoms attain the outer- shell noble gas configurations as a
result of the sharing of electrons.
Coordinate Bond (Dative Bond):
The bond formed between two atom in which contribution of an electron
pair is made by one of them while the sharing is done by both.
(i) 
?
4
NH (ammonium ion)
N
x
x
H
? x
H
x ?
H
?
x H
+
H ? N ? H
|
H
|
H
+
    Donor        Acceptor
(ii) O
3
 (ozone) or
O
O
O
Other examples : H
2 
SO
4
 , HNO
3
  , H
3
O
+
 , N
2
O, [Cu(NH
3
)
4
]
2+
Page 4


  
CHEMICAL BONDING
Chemical Bond :
 In the process each atom attains a stable outer electronic configuration
of inert gases.
Ionic or Electrovalent Bond :
The formation of an ionic compound would primarily depends upon :
* The ease of formation of the positive and negative ions from the respective
neutral atoms.
* The arrangement of the positive and negative ions in the solid, that is the
lattice of the crystalline compound.
Conditions for the formation of ionic compounds :
(i) Electronegativity difference between two combining elements must be
larger.
(ii) Ionization enthalpy (M(g) ? M
+
(g) + e
?
) of electropositive element must be
low.
(iii) Negative value of electron gain enthalpy (X (g) + e
?
 ? X
?
(g)) of
electronegative element should be high.
(iv) Lattice enthalpy (M
+
(g) + X
?
 (g) ? MX (s)) of an ionic solid must be high.
Lattice Enthalpy :
The lattice enthalpy of an ionic solid is defined as the energy required to
completely separate one mole of a
solid ionic compound into gaseous constituent ions.
Factors affecting  lattice energy of an ionic compound :
(i) Lattice energy  ? 
1
r r
? ?
?
 where (r
+
 + r?
?
 
) = Inter-ionic Distance.
(ii) Lattice energy  ? Z
+
, Z
?
Z
+
 ? charge on cation in terms electronic
 
charge.
Z
?
 ? charge on anion in terms electronic
 
charge.
Determination of lattice energy :
Born-Haber Cycle :
It inter relates the various energy terms involved during formation of an
ionic compound.
It a thermochemical cycle based on the Hess?s law of constant heat
summation.
  
Hydration :
All the simple salts dissolve in water, producing ions, and consequently
the solution conduct electricity. Since Li
+
  is very small, it is heavily
hydrated. This makes  radius of hydrated Li
+
  ion   large and hence it
moves only slowly. In contrast, Cs
+
   is the least hydrated because of its
bigger size and thus the radius of the Cs
+
  ion is smaller than the radius of
hydrated Li
+
,  and hence hydrated Cs
+
  moves faster, and conducts
electricity more readily.
Hydrolysis :
Hydrolysis means reaction with water molecules ultimately leading to
breaking of O-H bond into H
+
 and OH
?
 ions.
Hydrolysis in covalent compounds takes place generally by two
mechanisms
(a) By Coordinate bond formation : Generally in halides of atoms having
vacant d-orbitals or of halides of atoms having vacant orbitals.
(b) By H-bond formation : For example in Nitrogen trihalides
General properties of ionic compounds :
(a) Physical state : At room temperature ionic compounds exist either in
solid state or in solution phase but not in gaseous state.
(b) Simple ionic compounds do not show isomerism but isomorphism is their
important characteristic.
e.g. ,  FeSO
4
 .7H
2
O | MgSO
4
 . 7H
2
O
(c) Electrical conductivity :
All ionic solids are good conductors in molten state as well as in their
aqueous solutions because their ions are free to move.
(d) Solubility of ionic compounds :
Soluble in polar solvents like water which have high dielectric constant
Covalent character in ionic compounds (Fajan?s rule) :
Fajan?s pointed out that greater is the polarization of anion in a molecule,
more is covalent character in it.
More distortion of anion, more will be polarisation then covalent
character increases.
  
Fajan?s gives some rules which govern the covalent character in the ionic
compounds, which are as follows:
(i) Size of cation : Size of cation ? 1 / polarisation.
(ii) Size of anion : Size of anion ? polarisation
(iii) Charge on cation : Charge on cation ? polarisation.
(iv) Charge on anion :  Charge on anion ? polarisation.
(v) Pseudo inert gas configuration of cation :
Covalent Bond :
It forms by sharing of valence electrons between atoms to form molecules
e.g., formation of Cl
2
 molecule :
Cl Cl
Cl Cl
+
8e
?
8e
?
or Cl ? Cl
Covalent bond between two Cl atoms
The important conditions being that :
(i) Each bond Is formed as a result of sharing of an electron pair between the
atoms.
(ii) Each combining atom contributes at least one electron to the shared pair.
(iii) The combining atoms attain the outer- shell noble gas configurations as a
result of the sharing of electrons.
Coordinate Bond (Dative Bond):
The bond formed between two atom in which contribution of an electron
pair is made by one of them while the sharing is done by both.
(i) 
?
4
NH (ammonium ion)
N
x
x
H
? x
H
x ?
H
?
x H
+
H ? N ? H
|
H
|
H
+
    Donor        Acceptor
(ii) O
3
 (ozone) or
O
O
O
Other examples : H
2 
SO
4
 , HNO
3
  , H
3
O
+
 , N
2
O, [Cu(NH
3
)
4
]
2+
  
Formal Charge :
  
Formal charges help in the selection of the lowest energy structure from a
number of possible Lewis structures for a given species.
Limitations of the Octet Rule :
1. The incomplete octet of the central atom
LiCl, BeH
2
 and BCl
3
, AlCl
3
 and BF
3
.
2. Odd-electron molecules
nitric oxide, NO and nitrogen dioxide. NO
2
3. The expanded octet
      PF
5
        SF
6
H
2
SO
4
10 electrons around 12 electrons around 12 electrons around
the P atom the S atom the S atom
4. Other drawbacks of the octet theory
(i) some noble gases (for example xenon and krypton) also combine with
oxygen and fluorine to form a number of compounds like XeF
2 
 , KrF
2  
,
XeOF
2
 etc.,
(ii) This theory does not account for the shape of molecules.
(iii) It does not explain the relative stability of the molecules being totally
silent about the energy of a molecule.
Page 5


  
CHEMICAL BONDING
Chemical Bond :
 In the process each atom attains a stable outer electronic configuration
of inert gases.
Ionic or Electrovalent Bond :
The formation of an ionic compound would primarily depends upon :
* The ease of formation of the positive and negative ions from the respective
neutral atoms.
* The arrangement of the positive and negative ions in the solid, that is the
lattice of the crystalline compound.
Conditions for the formation of ionic compounds :
(i) Electronegativity difference between two combining elements must be
larger.
(ii) Ionization enthalpy (M(g) ? M
+
(g) + e
?
) of electropositive element must be
low.
(iii) Negative value of electron gain enthalpy (X (g) + e
?
 ? X
?
(g)) of
electronegative element should be high.
(iv) Lattice enthalpy (M
+
(g) + X
?
 (g) ? MX (s)) of an ionic solid must be high.
Lattice Enthalpy :
The lattice enthalpy of an ionic solid is defined as the energy required to
completely separate one mole of a
solid ionic compound into gaseous constituent ions.
Factors affecting  lattice energy of an ionic compound :
(i) Lattice energy  ? 
1
r r
? ?
?
 where (r
+
 + r?
?
 
) = Inter-ionic Distance.
(ii) Lattice energy  ? Z
+
, Z
?
Z
+
 ? charge on cation in terms electronic
 
charge.
Z
?
 ? charge on anion in terms electronic
 
charge.
Determination of lattice energy :
Born-Haber Cycle :
It inter relates the various energy terms involved during formation of an
ionic compound.
It a thermochemical cycle based on the Hess?s law of constant heat
summation.
  
Hydration :
All the simple salts dissolve in water, producing ions, and consequently
the solution conduct electricity. Since Li
+
  is very small, it is heavily
hydrated. This makes  radius of hydrated Li
+
  ion   large and hence it
moves only slowly. In contrast, Cs
+
   is the least hydrated because of its
bigger size and thus the radius of the Cs
+
  ion is smaller than the radius of
hydrated Li
+
,  and hence hydrated Cs
+
  moves faster, and conducts
electricity more readily.
Hydrolysis :
Hydrolysis means reaction with water molecules ultimately leading to
breaking of O-H bond into H
+
 and OH
?
 ions.
Hydrolysis in covalent compounds takes place generally by two
mechanisms
(a) By Coordinate bond formation : Generally in halides of atoms having
vacant d-orbitals or of halides of atoms having vacant orbitals.
(b) By H-bond formation : For example in Nitrogen trihalides
General properties of ionic compounds :
(a) Physical state : At room temperature ionic compounds exist either in
solid state or in solution phase but not in gaseous state.
(b) Simple ionic compounds do not show isomerism but isomorphism is their
important characteristic.
e.g. ,  FeSO
4
 .7H
2
O | MgSO
4
 . 7H
2
O
(c) Electrical conductivity :
All ionic solids are good conductors in molten state as well as in their
aqueous solutions because their ions are free to move.
(d) Solubility of ionic compounds :
Soluble in polar solvents like water which have high dielectric constant
Covalent character in ionic compounds (Fajan?s rule) :
Fajan?s pointed out that greater is the polarization of anion in a molecule,
more is covalent character in it.
More distortion of anion, more will be polarisation then covalent
character increases.
  
Fajan?s gives some rules which govern the covalent character in the ionic
compounds, which are as follows:
(i) Size of cation : Size of cation ? 1 / polarisation.
(ii) Size of anion : Size of anion ? polarisation
(iii) Charge on cation : Charge on cation ? polarisation.
(iv) Charge on anion :  Charge on anion ? polarisation.
(v) Pseudo inert gas configuration of cation :
Covalent Bond :
It forms by sharing of valence electrons between atoms to form molecules
e.g., formation of Cl
2
 molecule :
Cl Cl
Cl Cl
+
8e
?
8e
?
or Cl ? Cl
Covalent bond between two Cl atoms
The important conditions being that :
(i) Each bond Is formed as a result of sharing of an electron pair between the
atoms.
(ii) Each combining atom contributes at least one electron to the shared pair.
(iii) The combining atoms attain the outer- shell noble gas configurations as a
result of the sharing of electrons.
Coordinate Bond (Dative Bond):
The bond formed between two atom in which contribution of an electron
pair is made by one of them while the sharing is done by both.
(i) 
?
4
NH (ammonium ion)
N
x
x
H
? x
H
x ?
H
?
x H
+
H ? N ? H
|
H
|
H
+
    Donor        Acceptor
(ii) O
3
 (ozone) or
O
O
O
Other examples : H
2 
SO
4
 , HNO
3
  , H
3
O
+
 , N
2
O, [Cu(NH
3
)
4
]
2+
  
Formal Charge :
  
Formal charges help in the selection of the lowest energy structure from a
number of possible Lewis structures for a given species.
Limitations of the Octet Rule :
1. The incomplete octet of the central atom
LiCl, BeH
2
 and BCl
3
, AlCl
3
 and BF
3
.
2. Odd-electron molecules
nitric oxide, NO and nitrogen dioxide. NO
2
3. The expanded octet
      PF
5
        SF
6
H
2
SO
4
10 electrons around 12 electrons around 12 electrons around
the P atom the S atom the S atom
4. Other drawbacks of the octet theory
(i) some noble gases (for example xenon and krypton) also combine with
oxygen and fluorine to form a number of compounds like XeF
2 
 , KrF
2  
,
XeOF
2
 etc.,
(ii) This theory does not account for the shape of molecules.
(iii) It does not explain the relative stability of the molecules being totally
silent about the energy of a molecule.
  
Valence bond theory (VBT) :
H
2
(g) + 435.8 kJ mol 
?
 ? H(g) + H(g)
Orbital Overlap Concept
according to orbital overlap concept, the formation of a covalent bond
between two atoms results by pairing of electrons present, in the valence
shell having opposite spins.
Types of Overlapping and Nature of Covalent Bonds
The covalent bond may be classified into two types depending upon the
types of overlapping :
(i) sigma(?) bond, and  (ii) pi (?) bond
(i) Sigma (?) bond : This type of covalent bond is formed by the end to end
(head-on) overlap of bonding orbitals along the internuclear axis.
? s-s overlapping
? s-p overlapping:
? p-p overlapping : This type of overlap takes place between half filled
p-orbitals of the two approaching atoms.