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ICSE, State Boardsand EntranceExams.PreparedbyAlpha Education,
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1. ChemicalBond : Itis the
forcewhichholds theatomstogether inamolecule.
Thecauses of formationof bondare (i)
Tendencyof atomsto
comp lete theiroctets or
duplets byrearrangementof their valenceelectrons (octettheory).
(ii) Thesystemacquiresminimumenergy when
atoms are at some equilibrium distance where attractive forces
dominate over repulsive forces.
2. Types :BondChemical
BondIonic
BondCovalent BondMetallic BondordinateCo
3. Ionic Bond :4 It is theelectrostaticforce of attraction
betweenoppositelycharged ionswhich areformed
bycompletetransferenceof
electrons from one atom to another to get complete octet or
duplet.a)1 Favourable conditions to form ionic bond :
Formed between electro positive element (group 1, 2, 13) and
electro negative element group (15, 16, 17) 2 N.E Lower I.E of one
atom and more negative Ege of second atom 1 Higher lattice energy..
Larger cations, smaller anions.
b) Properties :Crystalline,
strongerforce of
attraction,thermallystable,lowvolatility,highdensity,
high m.pand b.p,highlyslouble inpolarsolvent,good
conductor of electricity in molten or solution state,
nondirectional bond .
. Covalent Bond :Covalent bond is formed by sharing of electrons
by two atoms to complete their octet or duplet. (octet theory)a)1
Favourable conditions to form covalent bond :
Formed between two electronegative elements (group 14, 15, 16,
17 ) 9.1 N.E
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5 Bond Length: It is the average distance betwen the nuclei of
two bonded atoms. It depends uponSize of the atom : Bond Length
increases with increase in the size of atom HFHBr ( >
)CCC =
Type of hybridisation : More s-character,shorter is thebond
length,greater is theacidity withcomparablecompound.
.
7 BondAngle : Itis
theinternalanglebetwentheorbitalscontainingelectronpairs
inthevalenceshell of centralatom in amolecule
More lone pairs on central atom, smaller is the bond angle due
to lp - bp repulsion.More electronegative central atom, more is the
bond angle.More electronegative surrounding atom, less is the bond
angle.
. sonance :In somemoleculesall thepropertiescannot be
explainedby singlestructureand themolecule issupposedto
havemany
and theactualstructure isinbetween of
all thesestructures,calledresonancehybrid. Thisphenomenonis
calledresonance.Main features
(a)1Differentstructureshavesamepositionsof
atoms,almostequalenergies,samenumber of
sharedandunsharedelectrons.
(c)1Resonating structures are imaginary.
(e)1More the number of canonical forms of nearly same energy,
greater is the stability of molecule.
. alence Bond Theory (VBT)
verlapping of atomic orbitals of valence shell of two atoms
leads to formation of a covalent bond.H
bond is formed by lateral overlapping. p,s p bond formation
nos
bond and bond is non-directional.
The direction of bond is same as the direction of overlapping of
orbitals. The strength of p ps
2 .
a)1 Valence shell electron pair repulsion (VSEPR) theory : Main
postulates of this theory are
Thus the molecule will have minimum energy and maximum
stability.
e. g. 4 , etc.
of molecule is unsymmetrical or it has irregular geometry.
Lonepair-lonepair>lonepair-bondpair>bond pair - bond
pair.2 3 4 5 6 7
Pentagonalbipyramidal
redistribution of their energies to form new orbitals of
identical shape and equal energy.N
brid orbitals form -
brid orbitals tend to remain far apart, therefore, replusion
order is bplplp >> .
= Number of its
ifferent types of hybridization are 333 d,spdspspspHy
