y rsl~ kQYX`n~w q sQl~v` rs`yn vQq&` aAXy k#lNQy …..."SOMETIMES IT SEEMS to me that a...

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)