Chemical Bonds Ionic Bonds Transfer of electron from metal to non metal Metal donate e Non Metal accept e Positive ion (cation) Negative ion (anion) Ionic compound Covalent Bonds Sharing of electron bet non metal atoms Equal sharing electrons + - electrostatic forces attraction 4 0.4 0 Difference in electronegativity 2 EN - 0.9 EN – 3 Diff = (3 – 3 ) = 0 H EN – 2.1 Diff = 3 – 0.9 = 2.1 Polar covalent Bonds Non Polar covalent Bonds Unequal sharing electrons Covalent Polar Non polar CI CI EN – 3 Covalent Non polar CI Covalent polar Ionic EN – 3 Diff = (3 – 2.1 ) = 0.9 Na + CI - EN – 3
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IB Chemistry on Polarity, Hydrogen Bonding and Van Der Waals forces
IB Chemistry on Polarity, Hydrogen Bonding and Van Der Waals forces
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Chemical Bonds
Ionic Bonds
Transfer of electron from metal to non metal
Metal donate e Non Metal accept e
Positive ion (cation)
Negative ion (anion)
Ionic compound
Covalent Bonds Sharing of electron bet non metal atoms
Equal sharing electrons
+ - electrostatic forces
attraction
4 0.4 0 Difference in electronegativity
2
EN - 0.9 EN – 3
Diff = (3 – 3 ) = 0
H
EN – 2.1
Diff = 3 – 0.9 = 2.1
Polar covalent Bonds Non Polar covalent Bonds
Unequal sharing electrons
Covalent Polar Non polar
CI CI
EN – 3
Covalent Non polar
CI
Covalent polar Ionic
EN – 3
Diff = (3 – 2.1 ) = 0.9
Na+ CI-
EN – 3
Shared electron cloud closer to O
Electronegativity
Electronegativity (EN) •Tendency of atom to attract/pull shared/bonding electron to itself •EN value higher – pull/attract electron higher (EN value from 0.7 – 4)
Electronegativity • EN increase up a Group • EN increase across a Period
H 2.2
Li Be B C N O F
CI
Br
I
1 1.6 2 2.6 3 3.4 4
Electronegativity values
N, O, F have high EN value
3.2
3
2.7
Molecule Diff in EN Polarity
H - F (4.0 – 2.2) = 1.8 Most polar
H - CI (3.2 – 2.2) = 1
H - Br (3.0 – 2.2) = 0.8
H - I (2.7 – 2.2) = 0.5 Least polar
Polarity
Shape Diff in EN
Symmetrical Asymmetrical
Bond polarity cancel out each other
Polar bonds – molecule NON POLAR
Bond polarity cancel out each other
Polar bonds – molecule POLAR
Lewis structure
VSEPR
Geometry
1
4 ECC
3 bond pair
1 lone pair
.. N
H H
H
Polarity
2
3
4
Polar
✓ ✗
✗
In presence of electric field
Separation of charges
Unequal distribution electron due to diff EN value
shared electron closer to O shared electron closer to F
Covalent Bonds
Polar covalent Bonds Non Polar covalent Bond
Equal sharing electron Unequal sharing electron
Sharing of electron
Formation electric dipole
Partial +/-
Dipole moment
towards O
Partial + ( δ+)
Partial – (δ−)
Net dipole moment
Molecule is polar (dipole)
Net Dipole moment
Measured in Debye
Turning force / Dipole moment = Force x Distance Polar covalent Bonds
+ - O
III
C δ+
δ-
Turning force – dipole moment
+ -
O
II
C
II
O
δ+
δ-
δ-
No Turning force – No dipole moment
✓
Molecule polar ✓
O
O
Polarity
Shape
Asymmetrical
Polar bond Polarity dont cancel (ASYMMETRICAL)
Net dipole moment Molecule POLAR
Polar bond Polarity cancel (SYMMETRICAL) NO net dipole moment Molecule NON POLAR
Shape
Symmetrical
Polar bonds
CI Polar bonds
δ-
δ+ δ+
δ+
δ-
δ-
δ-
δ-
δ-
δ-
Bond polarity
don’t cancel
Bond polarity
cancel
H
Net Dipole moment No Net Dipole moment
✗
Asymmetrical Symmetrical
δ- δ+
Polar bonds
Bond polarity
don’t cancel
Net Dipole moment
C O
Polar bond Polarity dont cancel (ASYMMETRICAL)
Net dipole moment Molecule POLAR
δ- δ-
Polar bonds
Bond polarity cancel
No Net Dipole moment
Polar bond Polarity cancel (SYMMETRICAL)
NO dipole moment Molecule NON POLAR
✗ ✗ ✓ ✓
I
Bonding Forces
Bonding Forces within molecule Bonding Forces bet molecule
Intermolecular force bet molecule (IMF) Ionic bond
Covalent bond
Metallic bond
Permanent dipole
Ions Molecules/NOT ions
Ion dipole forces
Polar Non Polar
Hydrogen bonding
Temporary dipole (instantaneously induced dipole) London dispersion forces
Van Der Waals’ Forces attraction
Polar molecule (dipole – dipole attraction)
_ _ _
Attraction bet ions with polar molecules
Dipole/dipole attraction Dipole/dipole attraction
(involving H atom attach to N,O F)
Hydrogen bonding (dipole – dipole attraction)
Forces bet molecule
Permanent dipole
Polar Non Polar
Temporary dipole (instantaneously induced dipole) London dispersion forces
Van Der Waals’ Forces attraction
Polar molecule (dipole – dipole attraction)
Polar molecules due to diff in EN values
Dipole/dipole interaction
Electrostatic forces attraction bet molecules
Dipole/dipole attraction Dipole/dipole attraction
Hydrogen bonding (dipole – dipole attraction)
H atom bond to electronegative atom, N, O, F
Partial H+ attracted to lone pair electron on N, O, F
Electrostatic force attraction bet molecules involve H
Intermolecular force bet molecule (IMF)
Non Polar molecule (Induced dipole attraction)
Random movement /distribution of electron
Instantaneous negative charge on atom
Induced a temporary dipole separation
Electrostatic forces attraction bet molecules
Non polar molecules
Polar molecules Polar molecules
Forces bet molecule
Molecules
Hydrogen bonding (dipole – dipole attraction)
H atom bond to electronegative atom, N, O, F
Partial H+ attracted to lone pair electron on N, O, F
Electrostatic force attraction bet molecules involve H
Permanent dipole
Polar Non Polar
Temporary dipole (instantaneously induced dipole) London dispersion forces
Van Der Waals’ Forces attraction
Polar molecule
Polar molecules due to diff in EN values
Dipole/dipole interaction
Electrostatic forces attraction bet molecules
Dipole/dipole attraction Dipole/dipole attraction
Molecules
Non Polar molecule (Induced dipole attraction)
Random movement /distribution of electron
Instantaneous negative charge on atom
Induced a temporary dipole separation
Instantaneous dipole in one atom
induce a dipole in its neighbor
Electrostatic forces attraction bet molecules
Non polar molecules Polar molecules
Polar molecules
Requirement for H bonding
•H atom bonded to N, O, F
•N, O, F - highly electronegative/ small size
•Attract electron close to itself – Polarised H+
•N---H, O—H, F—H bonds VERY POLAR
•Very polar H+ attract closely to lone pair on N, O, F
N ---- H O ---- H F ---- H δ- δ- δ- δ+ δ-+ δ+
Types of forces/Bonding
Factors affecting VDF forces Intermolecular force bet molecule (IMF)