Post on 17-Feb-2016
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Covalent Bonding• What’s going on?• Molecule – formed when 2 or more atoms
bond covalently
Sharing of electrons
Two Types of Covalent Bondsi) nonpolar covalent – equal sharing of e-
ii) polar covalent – UNequal sharing of e-
Nonpolar vs. Polar
NONPOLAR POLAR
Nonpolar vs. Polar
Nonpolar vs. Polar
Predict these shapes
N•• HH
H
NH3
trigonalpyramidal
H2O CO2
O••
••H H
bent
C••••O O•• ••
linear
Using electronegativity to determine bond type• Recall electronegativity: how much an
atom wants electrons
• Each atom is assigned a number between 0-4.0 to determine electronegativity strength
• We know 3 types of bonds:- nonpolar covalent- polar covalent- ionic
• To determine bond type, subtract electronegativity values and see scale
Using electronegativity to determine bond type
Scale
0 4.01.70.3
polarcovalent
nonpolarcovalent ionic
H-H
H-O
2.2 – 2.2 = 0
3.44 – 2.2 = 1.24
nonpolar
polar
H-C 2.55 – 2.2 = 0.35 polar
K-F 3.98 – 0.82 = 3.16 ionic
Dipole Moment• defn – imbalance of electron density in a
covalent bond– Due to electronegativity of atoms
- (partial negative) = signifies more EN atom
+ (partial positive) = signifies less EN atom
= shows direction of dipole moment
Examples
H = 2.2C = 2.6N = 3.0Cl = 3.2O = 3.4F = 4.0
H O+ -
Cl C- +
N H- +
C F+ -
Intermolecular Forces• Defn – attractive forces between 2
molecules; weak compared to bonds
Intermolecular Forces• London Dispersion Forces – very weak,
exist in all molecules due to temporary shifts in the electron cloud
Electrons evenly distributed
Temporary dipole
London force
Intermolecular Forces• Dipole-Dipole – attraction between
oppositely charged regions of polar molecules
+ - +
-+
-
Intermolecular Forces• Hydrogen Bonding – special type of
dipole-dipole occurring btwn molecules that have a H bonded to either a N,O, or F of another molecule; strongest force
- Water is prime example
OHH
O
+ +
-
OHH
O
OHH
O
OHH
O
OHH
O OHH
O
hydrogenbond
+ +
-
+ +
-
Strength Ranking
Hydrogen > dipole-dipole > London