y rsl~ kqyx`n~w q sql~v` rs`yn vqq&` aaxy k#lnqy …..."sometimes it seems to me that a...
TRANSCRIPT
a`c`r\y rsl~ kQYX`n~w q sQl~v`
rs`yn vQq&` aAXy
k#lNQy vQX~vvQq&`ly
rs`ynQk vQq&`v @ls ap hq`rn~@n~ kOmk~q?
rs`ynQk bn~{nyk~ ynE kOmk~q ?
~ 100 mRl qYv&y ~ mQlQyn15 ekQ@nkt
@vns~ sA@y`~g
"SOMETIMES IT SEEMS to me that a bond between two atoms has
become so real, so tangible, so friendly, that I can almost see it.
Then I awake with a little shock, for a chemical bond is not a real
thing. It does not exist. No one has ever seen one. No one ever can.
It is a figment of our own imagination.“
Charles Alfred Coulson (1910-1974) was an English theoretical chemist
who played a central role in the development of quantum theories of
chemical bonding.
prm`NEv (atom) Dalton’s Golf Ball model
Thomson’s Plum Pudding model
Rutherford’s model
Bohr model
i@lk~@tY`~n (kvc) vQxv Xk~wQy:
2s
2p
3s 3p
3d 4s 4p
1s
Xk
~wQ m
t|tm Aufbau principle
Hund’s Rule
Pauli Exclusion Principle
a;~Tk rWwQy
q`ny kQrW@mn~
lb` g#nW@mn~
@p`qE@v| wb` g#nW@mn~~
? i@lk~@tY`~n
aynQk a`kr\;N/bn~{n - Ionic Bonds
an~wr\ aNEk bl Intermolecular(nonbonded) forces
shsAyEj bn~{n - Covalent Bonds
aNEv
● ●
{Y#vWy shsAyEjw`v
mW@w~n~
sAgw(q`yk) bn~{n- Coordination bond
@l`~h bn~{n - Metallic bond
electropositive element + electropositive element
electropositive element + electronegative element
● ●
k`k~;Qk awQc|C`qny- orbital overlap
sQg~m` (s) bn~{n
pyQ(p) bn~{n
mEhEm|krNy sh mEhEm| k`k~;Qk Hybridization and hybrid orbitals
mW@w~n~ (Methane)
2s 2px 2pz 2py 1s sp3 sp3 sp3 sp3
109.5o
s#k#bEnE avs~}`v mEhEm|krNy
x
z
y
mW@w~n~ : k`bn~
xOmQ avs~}`v
CH2O
120o
2s 2px 2pz 2py 1s sp2 sp2 sp2
120o
mEhEm|krNy
@f ~̀m#l~dQhyQd| : k`bn~
120o
wlWy
wQY@k`~N`k`
r
2s + 2px + 2pz
2s 2px 2pz 2py 1s sp2 sp2 sp2
120o
mEhEm|krNy
@f ~̀m#l~dQhyQd| : ok~sQjn~
120o
wlWy
wQY@k`~N`k`r
e~~~~ksr
i@lk~@tY`~n
2s + 2px + 2pz
Formaldehyde
s bn~{ny 2 e~ksr yEgl p bn~{ny
m{& prm`NEv vt` pQhQtQ, bn~{n yEgl sh e~ksr
yEgl ekQ@nkQn~ h#kQw`k~ qErs~v sQtQn@s~ wQYm`n
avk`X@y~ k`]Qk pQhQtyQ.
v&Ehy (aNEvl h#d)
@r\KWy
uq`: BeCl2
wlWy wQY@k`~N`k`r
@k ~̀NWy
uq`: BF3
uq`: SO2
cwOs~wlWy
pQrmQdWy @k ~̀NWy @r\KWy
uq`: CH4
wQYy`nwQ q~vWpQrmQdWy
@r\KWy T h#dwQ sW-@s ~̀ h#dwQ
a;~TwlWy
cwOs~wlWy pQrmQd`k`r wlWy cwOs~r`k`r
pAc`XY q~vWpQrmQdWy
pAc`XY pQrmQd`k`r
2. A lone pair takes up more space around the central atom than a bond
pair. Hence repulsion between
lone pair – lone pair > bond pair-lone pair > bond pair-bond pair.
3. Magnitude of repulsion between bond pairs depend on the electro-
negativity difference between central atom and other atoms.
4. Repulsion by triple bonds > double bonds > single bonds
5. Lone pairs always adopt positions that minimize 90o interactions.
2s 2px 2pz 2py 1s sp sp
mEhEm|krNy
Hydrogen Cyanide: Carbon
2s + 2px
@r\KWy
2s 2px 2pz 2py 1s sp sp
mEhEm|krNy
Hydrogen Cyanide: Nitrogen
2s + 2px
@r\KWy
p bn~{ny s bn~{ny
p bn~{ny
Bond Polarity
polar covalent bond
The atoms involved in the covalent bond are from different elements, one of the
atoms will tend to attract the shared electrons more strongly, and the
electrons will spend more time near that atom.
non-polar covalent bond
atoms connected by a covalent bond are the same, neither atom attracts the
shared electrons more strongly than the other;.
Molecular dipole moments
• A molecule is polar if its centers of positive and negative
charge are separated.
• The dipole moment(m) is a measure of the degree of
polarity.
m = charge (q) x distance between the two centers (r)
• Polarity causes a neutral molecule to interact with ions or
other polar molecules.
Intermolecular(nonbonded) forces Molecules and ions are held together by attractive
forces weaker than normal bonds called
“intermolecular forces”.
• ion- ion- NaCl
• dipole – dipole – NF3
– Hydrogen bonds – H2O, HF,NH3
• ion – dipole-Na+ in water
• ion - induced dipole – Na+ with I2
• dipole – induced dipole- I2 in water
• London - CH4 - induced dipole-induced dipole
Van der Waals forces
• The attractive or repulsive force between molecules (or
between parts of the same molecule) other than those due to
covalent bonds or to the electrostatic interaction of ions with
one another or with neutral molecules.
• The term includes:
permanent dipole–permanent dipole forces
permanent dipole–induced dipole forces
instantaneous/induced dipole-induced dipole (London
dispersion forces)