Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Page # 3

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
...

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
...

Properties of ionic compounds :
 In the solid state, each cation surrounds itself with anions and each anion with cations
...

 They are good conductors of electricity in fused state or aqueous solution
...

 Have high melting point and boiling point than covalent compounds
...
e
...

Born-Haber cycle It is an indirect method to calculate the lattice energy of an ionic compound
...

1
Na(s) + Cl2(g)
NaCl(s)
2
S
+D/2
Na(g) +

+

Cl(g)

–

Na (g) + Cl (g)

–U

394 - Rajeev Gandhi Nagar Kota, Ph
...
0744-2209671, 93141-87482, 93527-21564
IVRS No
...
motioniitjee
...
com

Page # 4

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
...

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
...

(II) Atom/ion/molecule donating electron pair is called donor or Lewis base
...

Formation of NH4+ :
NH3 has three (N – H) bonds and one lone pair
...
This lone pair is donated to H+ ion
...

Valence Bond (V
...
Important
points of this theory are summarised below
...

(II) Half-filled orbitals should contain the electron with opposite spin
...

(IV) If the atomic orbitals overlap axially, then the bond formed is called a sigma () bond
...

(VI) Covalent bonds formed by the overlap of s-s and s-p orbitals are always sigma
...

(VIII)
Increasing strength of  covalent bonds is in the order s – s < s - p < p — p (when
internuclear distance is constant)
(IX) A single covalent bond is always a sigma bond
...
In a triple covalent bond, one is sigma and two are pi-bonds
...

Important features of hybridisation are given below
...
No
...
0744-2439051, 0744-2439052, 0744-2439053 www
...
com, email-info@motioniitjee
...

(II) The hybrid orbitals generated are equal in number to that of pure atomic orbitals which are
intermixed
...

(IV) Hybrid orbitals usually form sigma bonds
...

Valence shell electron pair repulsion (VSEPR) Theory (Gillespie theory) :
(I) The shape of a molecule is determined by repulsion between the electron pairs (p and bp) present
in the valence shell of the central atom
...
O
...
O
...
No
...
0744-2439051, 0744-2439052, 0744-2439053 www
...
com, email-info@motioniitjee
...

(III)Two types of molecular orbitals are formed
...

(b) Anti - bonding molecular orbitals at a higher energy than the combining atomic orbitals which
opposes the bond formation
...

Atomic orbitals
Bonding M
...

Anti-bonding M
...

1s + 1s
 1s
* 1s
2s + 2s
 2s
* 2s
2px + 2px
 2px
* 2px
2py + 2py
 2py
* 2py
2pz + 2pz
 2pz
* 2pz
Electrons are filled in the increasing order of energy of the molecular orbitals which is in order of Aufbau
rule
(a) When total electrons in the molecule or ions are more than 14(simple order of energy level
of M
...


(b) When total number of electrons in the molecule are ions are 14 (modified order of energy
level of M
...


(I) The electrons are filled in molecular orbitals in the same way as in atomic orbitals, that is, as per
the Hund’s Rule, Pauli exclusion principle and Aufbau rule
...
O
...

(III)For a stable molecule/ion, NB > NA
(IV) A given molecule or ion is paramagnetic if it has unpaired electrons in the molecular orbital
...
Thus for O2, O2 + ,
O2—,O22–
+

O2

–

O2

O2

2–

O2

Increasing bond length
Increasing bond order

394 - Rajeev Gandhi Nagar Kota, Ph
...
0744-2209671, 93141-87482, 93527-21564
IVRS No
...
motioniitjee
...
com

Page # 7

CHEMICAL BONDING

Fajan’s Rule :
This rule is used to decide relative ionic & covalent character in a molecule
...

(II) larger the size of anion
...

(IV) ion does not have inert gas configuration but it possesses pseudo inert gas configuration (18
electrons in the ultimate shell)
...
Thus, CuCl is more covalent
than NaCl
...

(II) H-bonding is said to be formed when slightly acidic hydrogen attached to a strongly electronegative atom such as F, O and N is held with weak electrostatic forces by the non- bonded pair of electron
of another atom
...

(III)Of all the electronegative donor atoms, only F, O
...

(IV) The weak electrostatic interaction leading to the H-bond formation is shown by dashed(
...

(V) Greater the electronegativity difference, stronger is the H-bond
...
H > O
...
H
Intramolecular H-bonding ;
This type of H-bonding occurs when polar H and electronegative atom are present in the same
molecule
...


394 - Rajeev Gandhi Nagar Kota, Ph
...
0744-2209671, 93141-87482, 93527-21564
IVRS No
...
motioniitjee
...
com



---