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Molecular Structure -all topics-reasoning,logical , analytical, thinking,...
UNIT 4
CHEMICAL BONDING AND MOLECULAR STRUCTURE
ns, etc.) together in different chemical species is called a chemical bond.
mical bonds.
ons (b) by sharing electrons.
he positive and negative ions was termed asthe electrovalent bond. The electrovalence is thus equal to the number of unit charge(s) on the ion.Ionic bond is favoured by (a) low ioni
electrons from one atom to another (gaining or losing) or by sharing of valence electrons in order to have an octet in their valence shells. This is known as octet rule.
atoms.It may be polar ,
non-polar,single , multiple (double,triple).
d
iring of electrons b/w
atoms
milar or dissimilar
red pair(s) of
sm
olar
pounds
solids
p. with exceptions
ith exceptions
ter & in polar
polar solvents
with a few exceptions
cular reactions
n are low
low
may be defined as the difference between the number of valence electrons of that atom in an isolated or free state and the number of electrons assigned to that atom in the Lewis struc
.,
the energy of a molecule
to completely separate one mole of a solid ionic compound into gaseous constituent ions.For example, the lattice enthalpy of NaCl is 788 kJmol –1
clei of two bonded atoms in a molecule. Bond length = r A + rB . Bond length inversely related to multiplicity of bonds & s- character .
lectron pairs around the central atom in a molecule/complex ion. Bond angle is expressed in degree which can be experimentally determined by spectroscopicmethods.
ticular type between two atoms in a gaseous state. The unit of bond enthalpy is kJ mol–1 . For example, the H – H bond enthalpy in hydrogen molecule is 435.8 kJ mol–1. Shorter the
ecule.
d O22– have bond order 1.N2, CO and NO+ have bond order 3
ely, a number of structures with similar energy, positions of nuclei, bonding and non-bonding pairs of electrons are taken as the canonical structures of the hybrid which describes th
ble will be the molecule in comparision to cononical forms.Due to resonance bond lengths become equal.e.g in benzene all C-C bonds are equal (1.39 Ao ) in ozone O-O bond
and the distance between the centres of positive and negative charge. It is usually designated by a Greek letter ‘μ’. Mathematically, it is expressed as follows :
usually expressed in Debye units (D).The conversion factor is 1 D = 3.33564 × 10
–30
Cm. Net dipole moment in water is 1.85 D.
h others effect.
RY
–Bond pair (bp
y end to end overlapand (ii) pi(π) bond; formed by sidewise overlap
ewise overlap
is unsymmetrical
he shape
along with a sigma
f overlaping
ly different energies so as to redistribute their energies, resulting in the formation of new set of orbitals nof equivalent energies and shape. For example when one 2sand three 2p-orb
-------------Hybrid Orbitals
get hybridised.
mic orbitals.
minimum repulsion between electron pairs and thus a stable arrangement. Therefore, the type of hybridisation indicates the geometry of the molecules
n. In some cases, even filled orbitals of valence shell take part in hybridisation.
d
s
Examples
Shape of
molecules
Bond
angles (in
degrees )
Linear
180 0
BeCl2 ,BeF2 ,
ZnCl2 , HgCl2
, C2 H2
Trigonal
planar
120 0
BF3 , BCl3 , C2
H4 , CO32- ,
NO 3 -
Tetrahedral
109. 5 0
CH 4 , CCl4
, SiCl4 , NH 4+
, ClO 4 -
Square
planar
90 0
-
Trigonal 120 0 & 90
0
bipyramidal
Octahedral
90 0
Pentagonal 72 0 & 90 0
bipyramidal
[Ni (CN)4 ]
,
[
PtCl4 ]
PCl 5 , PF 5
SF 6
IF 7
Percentage Percentage Examples
of sof pcharacter character
25 %
75 %
CH 4 , C2H6
33.3 %
66.6 %
C2H4
50 %
50 %
C2H2
< triple bond
< triple bond
> triple bond
< triple bond
bile in nature.
number of electrons present in the bonding and the antibonding orbitals Bond order (b.o.) = ½ (Nb–Na)
Remarks
highly unstable or does not exit
highly unstable or does not exit
its but is unstable
ngle bond (──)
ouble bond ( ═ )
ple bond ( ≡ )
roportional to bond dissociation
proportional to bond length
Molecule/ Total
S.No.
Ion
e-
1
H2
2
2
H2 +
3
H2 -
Confi
(σ
(σ
3
(σ1s)
4
He2
4
(σ1s)2
5
He2 +
3
(σ1s)
6
He2 -
5
(σ1s)2 (σ
7
Li2
6
(σ1s)2 (σ
8
Be2
8
KK[(σ 2
9
B2
10
KK[(σ 2s)2 (
2
10
C2
12 KK[(σ 2s)2 (σ
2px2=
11
N2
14
KK[σ 2s2<σ
π2py2
12
N2+
13
KK[σ 2s2<σ
π2py
13
N2-
15
K
2s2<σ*2s2<
2px2= π2py2)
14
N22-
16
15
O2
16
KK[σ 2s2<σ
π2py2)
*2px1
KK [σ 2s2<σ
2px2=
*2px1=
16
O2 +
15
KK [σ 2s2<σ
2px2= π2p
17
O2 -
17
KK [σ 2s2<σ
2px2= π2py
*2
18
O2 2-
18
KK [σ 2s2<σ
2px2= π2p
*2
19
F2
18
nthalpy (d) sigma bond & pi bond ?
shape of PCl5 using VSEPR theory.
Explain.
different shapes. Discuss.
reases from HF to HI.
have non-polar bonds? Justify.
sonance and two consequences of resonance.
, O2- , O22- molecular species w.r.t. their bond order , dissociation enthalpy , bond length ,
N2- , N22- molecular species w.r.t. their bond order, dissociation enthalpy , bond length , stability
ond length, stability of a molecule?
overlap of (a) two s- orbitals (b) end on overlap of two p- orbitals (c) sidewise overlap of two p-
lar orbitals (b) bonding and antibonding molecular orbitals.
i) bond angle (iv) bond order, (v)sigma bond (vi)pi bond(vii) polar bond (viii) Non-polar bond
how many water molecules are attached to each water molecule and in what direction?
atoms when :-
single bond compounds?
ctional?
have considerable dipole moments. Why?
f (i) PCl5 (ii) IF7 (iii) SF6(iv) H2O (v) NH3 (vi) CH4 (vii)
OF4 (xii) XeO2F2 (xiii) XeO3 (xiv) XeO4 (xv) BF3 (xvi) NH4+ (xvii) SO4 2-
olecular orbital theory (ii)Energies of molecular orbital (iii)Conditions for hybridization
r combination of atomic orbitals.
pt is useful in deciding the most suitable Lewis structure of a molecule or ion?
molecule(ii)Carbonate ion
(iii)Nitrate ion
om & number of sigma and pi -bonds in the
ii)CH3 –CH =CH – CH3
≡CH (vii) CH2 ═CH2(viii) CH3─CH3 (ix) Diamond
PART-A
ements : Mg, Na, B, O, N, Br.
:
and ions: H2S, SiCl4, BeF2
.
bond.
VSEPR model:
storted tetrahedral, bond
d order ?
e van der Waals forces?
bond order of : N2, O2, O2+ and O2
ules do not exist ?
gen bond ?
-
?
py than N2+ whereas O2+ has
hich one has a greater directional orientation and why ?
s & types.
l Theory).
llowing cases and why?
PART - B
SANJEEV KUMAR (PGT-CHEMISTRY)
K.V. YOL CANTT (H.P.)
NDING AND MOLECULAR STRUCTURE
O4 .
N,Br .
n in ozone.
ions.
formation.
ample.
alent radius (iii) bond angle (iv) bond enthalpy (v) bond order (vi)van der’Walls radius with an
r?
nce to CO3 2-.
C6H6 ,CO , CO2 , SO4 2-.
giving suitable examples.
i) CO2 (ii) SO2 (iii) H2O (iv) NO2
?
oment & Why?
nt chracter of ionic bonds.
.
ent although the Be-H bonds are polar.
y of following molecules (i) BeF2 (ii) BF3 (iii) CH4 (iv) SiF4 (v) NH3 (vi) NF3 (vii) H2O
xiii) PH3 (xiv) IF7 (xv) XeF2 (xvi) XeF4(xvii) XeF6 (xix) ) XeOF2 (xx) XeOF4
d tetrahedral but bond angle in water is less than that of ammonia.Discuss
ry?
sion do you draw about their structure?
of VBT.
halene?
d.
he following molecules (i)
C2H2 (ii)C2H4 (iii) C2H6
n?
s:- (i) BeF2 (ii) BF3 (iii) CH4 (iv) SiF4 (v) NH3 (vi) NF3 (vii) H2O (viii) PCl5 (ix) SF6
(xv) XeF2 (xvi) XeF4(xvii) XeF6 (xix) ) XeOF2 (xx) XeOF4 (xxi) C2H2
le.
ple.
ple.
y.
AO.
n of atomic orbitals?
olecular orbitals for N2and O2.
d order?
bonding molecular orbitals.
rogen(H2).
ot exit.
g species and indicate their bond order,stability,magnetic
an example.
mple.
mple.
properties (i) O2 , O2 + , O2 - , O2
2
+
, O2 - , O2 2- , N2 , N2 + , N2 - , N2 2- , Be2 , He2 , C2, H2 ,
ity and magnetic nature.
EV KUMAR (PGT-CHEMISTRY)
NTT (H.P.)
esonance & its features , hybridisation & its features & types , bond order . hydrogen bond &
n in representing the orbitals.
e axial bonds longer as compared to equatorial bonds ?
bond order of : N2, O2, O2+ and O2 2-
−
he following atoms to form
N.
he shape of H2O molecule is bent while that of CO2 is linear. Explain this on the basis of dipole
on gain enthalpy ?
nt bond.
r in the molecules: LiF, K2O, N2, SO2and ClF3
ombination of atomic orbitals to form molecular orbitals.
metry for CH4is square planar
C atom at its centre.
although the Be–H bonds are
nd why ?
cribe the shapes of sp, sp2,sp3 hybrid orbitals.
atom in the following reaction.
ms as a result of the following reaction ? BF3 + NH3 ----------------àF3BNH3
d and a triple bond between
ollowing molecules ?
f the following will not form
py2 and py (d) 1s and 2s.
following molecules ?
-CHO (e) CH3COOH
l 5 , BF 3
SEPR theory (b) Hybridisation.
H 2O .
amples ( two for each).