1 POLARITY  POLAR BONDS  Bonds between atoms  POLAR MOLECULES  Polarity between molecules  Occurs when polar bonds create a dipole moment

HCl is POLAR because it has a positive end and a negative end. Cl has a greater share in bonding electrons than does H. Cl has slight negative charge (-  ) and H has slight positive charge (+  )

Bond Polarity Which bond is more polar (or DIPOLAR)? O—HO—F O—HO—F   OH is more polar than OF OH is more polar than OF and polarity is “reversed.”

Molecular Polarity Molecules—such as HCl and H 2 O— can be POLAR (or dipolar). They have a DIPOLE MOMENT. The polar HCl molecule will turn to align with an electric field. Figure 9.15

Molecular Polarity Molecules will be polar if a)bonds are polar AND AND b)the molecule is NOT “symmetric” All above are NOT polar

Polar or Nonpolar? Compare CO 2 and H 2 O. Which one is polar?

Polar or Nonpolar? Consider AB 3 molecules: BF 3, Cl 2 CO, and NH 3.

Molecular Polarity, BF 3 B atom is positive and F atoms are negative. B—F bonds in BF 3 are polar. But molecule is symmetrical and NOT polar

Molecular Polarity, HBF 2 B atom is positive but H & F atoms are negative. B—F and B—H bonds in HBF 2 are polar. But molecule is NOT symmetrical and is polar.

Is Methane, CH 4, Polar?

Is CH 3 F Polar?

BONDING/FORCES INTRA MOLECULAR FORCES – Ionic – Covalent – Metallic INTER MOLECULAR FORCES – Van der Waal’s Forces London dispersion Dipole-Dipole Hydrogen Bonding

14 Bonding, Intermolecular Forces (IMF)  IMF < intra molecular forces (covalent, metallic, ionic bonds)  IMF strength: solids > liquids > gases  Boiling points and melting points are good indicators of relative IMF strength.

Summary of IMF Van der Waals forces

Types of Crystalline Solids TypeParticlesForces Notable properties Examples AtomicAtoms London dispersion  Poor conductors  Very low MP Ar (s), Kr (s)

TypeParticlesForces Notable properties Examples Molecular Molecules (polar or non-polar) London dispersion, dipole- dipole, H- bonds  Poor conductors  Low to moderate MP CO 2 (s), C 12 H 22 O 11, H 2 O (s) SucroseCarbon dioxide (dry ice) Ice

TypeParticlesForces Notable properties Examples Ionic Anions and Cations Electrostatic attractions  Hard & brittle  High MP  Poor conductors  Some solubility in H 2 O NaCl, Ca(NO 3 ) 2

TypeParticlesForces Notable properties Examples Covalent (a.k.a. covalent network) Atoms bonded in a covalent network Covalent bonds  Very hard  Very high MP  Generally insoluble  Variable conductivity C (diamond & graphite) SiO 2 (quartz) Ge, Si, SiC, BN Diamond Graphite SiO 2

TypeParticlesForces Notable properties Examples Metallic Metal cations in a diffuse, delocalized e - cloud / sea of e - Metallic bonds  Excellent conductors  Malleable  Ductile  High but wide range of MP Cu, Al, Fe