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?

H2O(l) H2O(g)

or

2 H2O(l) 2 H2(g) + O2(g)

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.

Intermolecular ForcesIdentify the type of IMFStrongest?

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

Why is glycerol more viscous than water?

Homework

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