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Bonding What exactly is a bond? Depends…Ionic or Covalent? Polar?
NON-POLAR COVALENT=> equal sharing of electron pair 0 <
∆EN < 0.4
POLAR COVALENT= unequal sharing of electron pairs, e-’s spend more time closer to one atom, 0.4 < ∆EN < 1.7
IONIC “BOND”= transfer of electrons, no physical connection to one another, atoms are held together by an electrostatic attraction, ∆EN > 1.7
No molecular dipole=> non-polar molecule
Molecular Polarity• Tutorial 1: p. 226• Figure 6: p. 228• p. 227 #1,2• HW: p. 229 #1-7ab
Molecular Dipole is present=> polar molecule
No molecular dipole=> non-polar molecule
Molecular Dipole is present=> polar molecule
Intermolecular ForcesLondon force (dispersion)•due to electrostatic attraction b/w protons in one molecule and electrons of neighbouring molecules•strength α # of e-
Cl2 bp = -35°CI2 bp = 84°CExplain the trend in bp.
Cl2 has 34 e-. I2 has 106 e-.I2 has more e- => greater LDF => higher bp
Intermolecular Forcesdipole-dipole force•due to attraction of one dipole by surrounding dipoles•strength α molecular polarity
CH2O bp = -21°CC2H6 bp = -89°CExplain the trend in bp.Include diagrams to supportyour explanation.
CH2O is a polar molecule => has a dipole force, LDF (16 e-)C2H6 is a non-polar molecule => no dipole force, only LDF (18 e-)CH2O has higher bp due to dipole-dipole force
Predict which substance has the stronger dipole force: HCl or HBr
HCl is the more polar molecule (ΔEN is greater) => stronger dipole forces
(Draw diagrams to support your explanation.)
Intermolecular ForcesHydrogen bonding•due to attraction of a H bonded to a highly EN atom (O, N or F) in one molecule by the lone pair of e- on a highly electronegative atom of a neighbouring molecule
H2Te bp = -10°CH2Se bp = -50°CH2S bp = -80°CH2O bp = 100°CExplain the trend in bp.
Properties of Liquids
Cohesive forces: • attractions b/w like
moleculesAdhesive forces:• attractions b/w unlike
molecules
Capillary Action
• Water is transported in thin tubes from roots to shoots.
• adhesive forces (b/w H2O and sides of tubes) and cohesive forces (b/w H2O molecules)
• Water is pulled up against gravity!
Intermolecular Forces and Propertiesi) Boiling and melting ptii) Surface tensioniii) Meniscus shapeiv) Capillary actionv) Volatilityvi) Viscosityvii) Solubility viii) Wetting Actionix) Hydrophobicity
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