Polarity in Covalent Polarity in Covalent Bonds Bonds Bonding Movie
Polarity in Covalent BondsPolarity in Covalent Bonds
Bonding Movie
Polar BondPolar Bond
• Polar – Polar – has poleshas poles
–ends are differentends are different–bonds: bonds: differencedifference in in how electrons how electrons
distributeddistributed–Polar bond: one end more electrons Polar bond: one end more electrons
than other endthan other end
Nonpolar BondNonpolar Bond
• NonNonpolar = NoNo poles
• electron cloud on one end of bond same as other end
HH22 is symmetric: is symmetric: Both Both ends the same; electron ends the same; electron cloud football-shapedcloud football-shaped
HCl is asymmetric:HCl is asymmetric: electron cloud electron cloud lopsided; Cl more lopsided; Cl more electrons than Helectrons than H
Which bond(s) are polar?Which bond(s) are polar?Which are nonpolar?Which are nonpolar?
Polar = LiH & HF Nonpolar = HPolar = LiH & HF Nonpolar = H22
Red = electron Red = electron richrich
Blue = electron Blue = electron poorpoor
How can predict How can predict if BOND is if BOND is polar or polar or nonpolar?nonpolar?
Compare electronegativities of two Compare electronegativities of two atoms in bondatoms in bond
ElectronegativityElectronegativity
Ability of atom to attract electrons in bond
Found inFound in Table S!Table S!
Electronegativities of the ElementsElectronegativities of the Elements
Bond PolarityBond Polarity
• more electronegative atom pulls bonding electrons more strongly & gets more than fair share of electron cloud
• Leads to separation of charge– electron-rich side is partially negative (-)– electron-poor side is partially positive (+)
Delta notationDelta notation
BOND PolarityBOND Polarity• Depends on electronegativity differencedifference
between two atoms in bond
A BA B EEAA - E - EBB
•- - care only aboutcare only about size of size of difference, not signdifference, not sign
•- - bigger the difference, the more polar the bondbigger the difference, the more polar the bond
Calculate Calculate electronegativity electronegativity difference for each difference for each of these bondsof these bonds
LiH : HLiH : H22 : HF: : HF: 2.1 – 1.02.1 – 1.0 1.11.1
2.1 – 2.12.1 – 2.1 00
2.1 – 42.1 – 4 1.91.9
Bond PolarityBond Polarity
• What can say about polarity of bond where atom A = atom B?
If both atoms are same element: If both atoms are same element: electronegativity difference = 0electronegativity difference = 0
Electronegativity DifferenceElectronegativity Difference
IonicIonic> 1.7> 1.7
Polar CovalentPolar Covalent>>0.5 to 1.70.5 to 1.7
Nonpolar CovalentNonpolar Covalent0.0 to 0.50.0 to 0.5
Type of BondType of BondElectronegativityElectronegativity DifferenceDifference
Electronegativity & Bond TypeElectronegativity & Bond Type
ReviewReview
• Which of following bonds is most polar?–A) O2
–B) HCl –C) NH in NH3
–D) HBr
3.4 – 3.4 = 03.4 – 3.4 = 02.1 – 3.2 = -1.1 = 1.12.1 – 3.2 = -1.1 = 1.1
3.0 – 2.1 = 0.93.0 – 2.1 = 0.93.0 – 2.1 = 0.93.0 – 2.1 = 0.9
Answer = (B) HClAnswer = (B) HCl
ReviewReview
• Which substance contains bond with greatest ionic character?– A) KCl– B) HCl– C) Cl2– D) CCl4
0.8 – 3.2 = -2.4 = 2.40.8 – 3.2 = -2.4 = 2.42.1 – 3.2 = -1.1 = 1.12.1 – 3.2 = -1.1 = 1.1
3.2 – 3.2 = 03.2 – 3.2 = 02.6 – 3.2 = -0.6 = 0.62.6 – 3.2 = -0.6 = 0.6
Answer = (A) KClAnswer = (A) KCl
SummarySummary
• Nonpolar covalent bonds form:– between atoms having equal or close
electronegativity values: 0.0 - 0.4
• Polar covalent bonds form: – between atoms with electronegativity
difference >0.5 to 1.7
Predict the PolarityPredict the Polarity
• N2
• HF• HCl• O2
• Cl2• HI• HBr
NonpolarNonpolarPolarPolarPolarPolar
NonpolarNonpolarNonpolarNonpolarPolarPolarPolarPolar
MOLECULE Polarity
• Diatomic molecules:– molecular polarity is same as bond polarity
MOLECULEMOLECULE Polarity (3 Polarity (3++ elements) elements)
• Depends on 2 factors1. Type bonds in molecule2. Arrangement of bonds or shape of
molecule
Think SYMMETRY!!
For larger molecules:For larger molecules:• look at kind & arrangement of bonds to look at kind & arrangement of bonds to determine overall polarity of moleculedetermine overall polarity of molecule
Polarity of MoleculesPolarity of Molecules
• molecule may contain polar bonds, but not be polar! – depends on geometry of molecule
• If molecule is symmetric:– “pull” of one polar bond is offset by “pull” of
another polar bond– tug-of-war that no one can win!
Symmetric MoleculesSymmetric Molecules
• Contain at least two mirror planes
Symmetric vs. Asymmetric
COCO22 is nonpolar is nonpolar - - electron cloud is symmetricelectron cloud is symmetric
HH22O is polar O is polar -- electron cloud is lop-sided (asymmetrical) electron cloud is lop-sided (asymmetrical)
Polarity of CO2?
Draw arrow along each bond pointing to Draw arrow along each bond pointing to more electronegative atommore electronegative atomIf arrows cancel out, molecule is If arrows cancel out, molecule is NONPOLARNONPOLAR
Polarity of H2O?
green arrows do green arrows do NOT cancel outNOT cancel out - water is polar!- water is polar!
structural formula can be used to predict Molecular Polarity!
HH
H H C C H H HH
Symmetry of Larger MoleculesSymmetry of Larger Molecules
CFCF44 is symmetric is symmetric so is nonpolarso is nonpolar
Ethane = CEthane = C22HH66
Ethene = CEthene = C22HH44
Ethyne = CEthyne = C22HH22
These molecules are symmetric - electron These molecules are symmetric - electron cloud is same on both ends: they are nonpolarcloud is same on both ends: they are nonpolar