Wednesday, October 17, 2018

MOLECULAR STRUCTURE AND CHEMICAL BONDING

MOLECULAR STRUCTURE AND CHEMICAL BONDING

Introduction


Bonding ;- It is the force of attraction which can bounded together called bonding In Chemistry bond formed by sharing of electron protons and opposite charges 
MOLECULAR STRUCTURE AND CHEMICAL BONDING
Types Of Bond 

1. Covalent Bond Bond formed by mutual sharing of electrons between the atoms
2. Ionic Bond Bond formed by transferring of valence electrons from one atom to another. 
3. Coordinate Bond A special type of covalent bond where shared pair of electrons is donated by one atom to other. 

Explained Ionic Bond

Ionic Bond Bond formed by transferring of valence electrons from one atom to another.

     Conditions Required : 

1. Electronegativity difference between the atoms must be high.

2. Low ionisation energy of the element forming cation and high electron  affinity of the element            forming anion. 
3, Lattice energy for formation of ionic compound must be high. 

4. ΔHf = ΔHs + IE + 1 2 ΔHd – EA – U where ΔHf = Enthalpy of formation,

 5. ΔHs = Enthalpy of sublimation, IE = Ionisation energy, ΔHd = Enthalpy of dissociation, EA =            Electron affinity and U = Lattice energy.

FAJAN’S RULE

It state that- the magnitude of covalent character in the ionic bond depends upon the extent of polarization    caused by cation. Smaller the cation, larger is its polarizing power. Larger the anion, more is its   polarisibility. 

VALENCE SHELL ELECTRON PAIR REPULSION THEORY (VSEPR) 

The best arrangement of a given number of electron  pairs is the one that minimises the repulsion among them. Repulsive interactions :  Lone pair - lone pair >  lone pair - bond pair > bond pair - bond pair Valence bond theory (VBT) : 

 The formation of a covalent bond is due to pairing of electrons present in the valence shell having opposite spins. Head on overlap of atomic orbitals gives σ bond, sideway overlap of atomic orbitals gives π bond

HYBRIDISATION

It State that- the process of intermixing of orbitals   with slightly different energies so as to redistribute their energies giving another set of orbitals  (called hybrid orbitals) with same energy, size and shap

The structure of any molecule can be predicted on  the basis of hybridisation by formula : No. of hybrid orbitals (H)

=1/2(No of valence electron of central atom)+(No of monovalent atom)-(Charge present on the cation)+(Charged present on anion)

Types of Hybridization
Orbitals mixed
Shape of the molecule/ion
Examples
sp
one s + one p
Linear
BeF2, BeH2, C2H2, HgCl2
sp2
one s + two p
Triangular planar
BF3, C2H4, NO3, CO23
sp3
one s + three p
Tetrahedral
CH4, CCl4, SnCl4, NH+4, [Ni(CO)4]
dsp2
one d d( 2           2 ) + one s + two p
x y
Square planar
[Ni(CN)4]2–, [PtCl4]2–
sp3d
one s + three p + one d d( 2)
z
Trigonal bipyramidal
PF5, PCl5
sp3d2
one s + three p + two d
(d 2              2 ,d 2) x y         z
Octahedral
SF6, [CrF6]3– [Co(NH3)6]3+
sp3d3
one s + three p + three d
(dxy,dyz,dxz)
Pentagonal bipyramidal
IF7

MOLECULAR ORBITAL THEORY 

1. The atomic orbitals of comparable energy and  proper symmetry combine to form equal number of       molecular orbitals. 

2. The  bonding molecular orbital has lower energy and greater stability than the corresponding               antibonding molecular orbital.

3. Bond order =  1 2
  (Nb – Na) [Nb = No. of bonding electrons, Na = No. of antibonding electrons] 

4, The order of energies of molecular orbitals for  simple homonuclear diatomic molecules like O2,        F2 and Ne2 is σ1s, σ∗1s, σ2s, σ∗2s, σ2pz, π2px = π2py, π∗2px = π∗2py, σ∗2pz 

5. The order of energies of molecular orbitals for  diatomic lighter elements like B2, C2 and N2 is           σ1s, σ∗1s, σ2s, σ∗2s, π2px = π2py, σ2pz, π∗2px ==π2py, σ2pz


HYDROGEN BONDING 

It state that- the attractive force which binds hydrogen atom   of one molecule with the electronegative atom  (F, O or N) of another molecule is called Hydrogen Bonding

It can be intermolecular (in case of HF, ROH or H2O) or intramolecular (in case of o-nitrophenol

METALLIC BONDING 

It state that the Metallic bond is electrostatic force of attraction  between positively charged kernels (nuclei with core electron) and mobile electrons which holds the metal atoms together.

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