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

Which process requires more energy? Why? H 2 O (l)  H 2 O (g) or 2 H 2 O (l)  2 H 2(g) + O 2(g)

Intermolecular Forces London force (dispersion) due to electrostatic attraction b/w protons in one molecule and electrons of neighbouring molecules strength α # of e - Cl 2 bp = -35°C I 2 bp = 84°C Explain the trend in bp. Cl 2 has 34 e -. I 2 has 106 e -. I 2 has more e - => greater LDF => higher bp

Intermolecular Forces dipole-dipole force due to attraction of one dipole by surrounding dipoles strength α molecular polarity CH 2 Obp = -21°C C 2 H 6 bp = -89°C Explain the trend in bp. Include diagrams to support your explanation. CH 2 O is a polar molecule => has a dipole force, LDF (16 e - ) C 2 H 6 is a non-polar molecule => no dipole force, only LDF (18 e - ) CH 2 O 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 Forces Hydrogen 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 H 2 Tebp = -10°C H 2 Sebp = -50°C H 2 Sbp = -80°C H 2 Obp = 100°C Explain the trend in bp.

Intermolecular Forces Identify the type of IMF Strongest? Identify the type of IMF Strongest?

Properties of Liquids Cohesive forces: attractions b/w like molecules Adhesive forces: attractions b/w unlike molecules

Capillary Action Water is transported in thin tubes from roots to shoots. adhesive forces (b/w H 2 O and sides of tubes) and cohesive forces (b/w H 2 O molecules) Water is pulled up against gravity!

Intermolecular Forces and Properties i)Boiling and melting pt ii)Surface tension iii)Meniscus shape iv)Capillary action v)Volatility vi)Viscosity vii)Solubility viii)Wetting Action ix)Hydrophobicity

Why is glycerol more viscous than water?

Homework Section 4.7 p. 244 #1,2 p. 247 #1-6