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CHEMICAL BONDING

CHEMICAL BONDING
KEY CONCEPTS
INTRODUCTION
A molecule will be formed if it is more stable and has a lower energy than the individual atom
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Types of Bonds :
Atoms involved
(I) Metal + Nonmetal
(II) Nonmetal + Nonmetal
(III)Metal + Metal
(IV) Electron deficient molecule or ion (Lewis acid) and
electron rich molecule or ion (Lewis base)
(V) H and electronegative elements (N, O, F some times with Cl)

Bonding
Ionic
Covalent
Metallic
Coordinate
Hydrogen

Ionic, Covalent and coordinate bonding
Ionic bonding
An ionic bond is formed when a metal atom transfers one or more electrons to a non-metal atom
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Properties of ionic compounds :
 In the solid state, each cation surrounds itself with anions and each anion with cations
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 They are good conductors of electricity in fused state or aqueous solution
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 Have high melting point and boiling point than covalent compounds
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e
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Born-Haber cycle It is an indirect method to calculate the lattice energy of an ionic compound
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1
Na(s) + Cl2(g)
NaCl(s)
2
S
+D/2
Na(g) +

+

Cl(g)

–

Na (g) + Cl (g)

–U

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CHEMICAL BONDING

Now, according to Hess’s law,

Hformation = S + IE1 + D/2 – EA1 – U
Where S is the enthalpy of sublimation of metal (Na), IE1 is the first ionisation energy of sodium, D is
the bond dissociation energy of Cl1 molecule, EA1 is the first electron affinity of Cl, U is the lattice
energy of NaCl(s) and Hformation is the enthalpy of formation of NaCl
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Coordinate Bonding or Dative Bond :
Whenever covalent bond is formed by unequal sharing of a pair of electrons between a Lewis base and
Lewis acid is called coordinate bond
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(II) Atom/ion/molecule donating electron pair is called donor or Lewis base
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Formation of NH4+ :
NH3 has three (N – H) bonds and one lone pair
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This lone pair is donated to H+ ion
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Valence Bond (V
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Important
points of this theory are summarised below
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(II) Half-filled orbitals should contain the electron with opposite spin
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(IV) If the atomic orbitals overlap axially, then the bond formed is called a sigma () bond
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(VI) Covalent bonds formed by the overlap of s-s and s-p orbitals are always sigma
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(VIII)
Increasing strength of  covalent bonds is in the order s – s < s - p < p — p (when
internuclear distance is constant)
(IX

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