Intra vs Inter

1. Intra vs Inter • The prefix intra- means “within” • The word intramural literally means “within walls”, and refers to things that occur within the walls of a school, or things that are self-contained. • Intraparticle forces act within a compound, such as covalent bonds.

2. Intra vs Inter • The prefix inter- means “between” or “among”. • The internet, as I think we’re all aware, covers the globe, and anyone with a connection can access it from anywhere in the world.  • Interparticleforces act betweencompounds, usually molecules. These are new types of forces that we will discuss today.

3. InterparticleForces Three types of force can operate between covalent molecules: • Dispersion Forces also known as London Forcesor as van der Waal's Forces. • Dipole-dipole • Hydrogen bonds (special type of dipole-dipole)

4. Relative Strength of Intermolecular Forces: Intermolecular forces are much weaker than intramolecular forces • dispersion forces are the weakest intermolecular force (one hundredth-one thousandth the strength of a covalent bond) • hydrogen bonds are the strongest intermolecular force (about one-tenth the strength of a covalent bond). • dispersion < dipole-dipole < hydrogen bonds

5. Dispersion Forces(London Forces, van der Waal's Forces) Very weak forces of attraction between molecules resulting from: • momentary dipoles occurring due to uneven electron distributions in neighbouring molecules as they approach one another. • the weak residual attraction of the nuclei in one molecule for the electrons in a neighbouring molecule. • The more electrons that are present in the molecule, the stronger the dispersion forces will be. • Dispersion forces are the only type of intermolecular force operating between non-polar molecules

6. Dipole-dipole Interactions Stronger intermolecular forces than Dispersion forces • occur between molecules that have permanent net dipoles (polar molecules). • The partial positive charge on one molecule is electrostatically attracted to the partial negative charge on a neighbouring molecule.

7. Hydrogen Bonds • occur between polar molecules that have a permanent net dipole resulting from hydrogen being covalently bonded to either fluorine, oxygen or nitrogen. • The dipole created between the hydrogen atom andthe fluorine, oxygen or nitrogen atom is extremely polar. • This creates ahighly localized positive charge on the hydrogen atom and highly negative localized charge on the fluorine, oxygen or nitrogen atom. • Responsible for high surface tension of water.

8. Effect of IntermolecularForces Melting and Boiling Points • melting or boiling results from a weakening of the attractive forces between the molecules. • the stronger the intermolecular force is, the more energy is required to melt the solid or boil the liquid.

9. Effect of Intermolecular Forces on Solubility In general like dissolves like: • non-polar compoundsdissolve in non-polar solvents • polar compoundssuch as sugar (glucose C6H12O6) will dissolve in polar solvents such as water (H2O) • ionic solutes such as sodium chloride (NaCl) will generally dissolve in polar solvents but not in non-polar solvents

10. Intermolecular Forces Worksheet • 1) Identify the main intermolecular force in the following compounds. You must determine compound polarity first. a) PF3 _____________________________ b) H2CO ___________________________ c) HF ______________________________

11. Homework • Read section 3.4 in the textbook to help support what we covered in class today. • Summary on page 114 • Page 115 #1-5