1. between

3.  Intra- › strong forces that hold the atoms in a molecule together  takes 464 kJ/mol to break the H-O bonds within a water molecule › responsible for chemical properties

4.  Inter- › weak forces that holds molecules to one another  takes only 19 kJ/mol to break the bonds between water molecules › the strength of the intermolecular forces determines the physical properties of the substance  melting, boiling, solubility, conductivity, volatility

5.  3 main “types” of intermolecular forces 1. London forces (also called dispersion forces or instantaneous induced dipole forces 2. dipole-dipole forces (polar molecules) 3. a stronger type of dipole-dipole bonding called hydrogen bonding * Van der Walls and London forces are often used interchangeably– more later on this. strength increases

10.  van der Waals’ YouTube (:20) van der Waals’ YouTube (:20)  occurs in all molecules, even diatomic molecules (HOFBrINCl)  the distribution of electrons around an individual atom, at a given instant in time, may not be perfectly symmetrical › this can produce temporary/instantaneous dipole (polar molecule) › this can then induce a nearby molecule to be polar and therefore a very weak attraction between the two molecules

12. › magnitude of the force depends on… 1.number of electrons and size of the electron cloud  with more electrons, valence electrons are farther away from the nucleus and can be polarized more easily 2.shape of molecules  molecules with shapes that have more contact area have greater forces between them than those don’t

13. boiling point increases this flat shape allows it to stick to one another better these round shapes do NOT allow them to stick to one another

14.  attractive forces between the positive end of one polar molecule and the negative end of another polar molecule  must be in close proximity for the dipole- dipole forces to be significant  the more polar the molecule, the greater the dipole-dipole force  stronger than London forces

19.  YouTube Hydrogen Bonding (1:40) YouTube Hydrogen Bonding (1:40)  YouTube Hydrogen Bonding Video (:58) YouTube Hydrogen Bonding Video (:58)  a specific type of dipole-dipole type interactions  stronger than other dipole-dipole and London forces  the hydrogen (H) in a molecule is inter molecularly bonded to a small, highly electronegative element (usually an N, O or F atom) on another molecule H-NOF

24.  Melting point (mp) - solid to liquid  Boiling point (bp) - liquid to gas  Volatility - how easily it is converted to gas  Conductivity (conducts electricity) › depends on whether the substance contains freely moving charged particles  Solubility - solute’s ability to dissolve in solvent

25.  the greater polarity of a molecule, the higher the boiling point › In HF, H is 2.1 and F is 4.0, difference of 1.9 › In HCl, H is 2.1 and Cl is 3.0, difference of 0.9 BP is 20°C BP is -85°C

26. › H 2 O vs. H 2 S?  In H 2 O, H is 2.1 and O is 3.5, difference of 1.4  water molecules can hydrogen bond (and London forces) to each other  BP is 100°C  In H 2 S, H is 2.1 and S is 2.5, only a difference of 0.4  H 2 S can dipole-dipole bond (and London forces) to each other  BP is -60°C H-NOF ? yes H-NOF ? no

27.  CH 3 OCH 3 vs. CH 3 CH 2 OH ?  -24°C 78°C dipole – dipole has hydrogen bonding H-NOF ?  NH 3 vs. PH 3 ?  -33°C -87°C has hydrogen bonding dipole – dipole

28.  CH 3 CH 2 CH 3 vs. CH 3 CHO vs. CH 3 CH 2 OH ? only London forces (VDW) low BP VDW & dipole-dipole medium BP VDW, D-D, & hydrogen bonding highest BP

30.  held tight by strong electrostatic forces in between cations and anions  non-volatile, high mp, high bp  solid at room temp  hard and brittle because of lattice/crystalline structure  conductivity › non-mobile e- as solid = no › ions move freely when melted = yes › cations and ions separate when dissolved in water = yes  soluble in polar solvents like water

31.  strong intramolecular forces, weak intermolecular forces, usually liquids or gases at room temp or soft solid › strength of polarity and strength of London forces determine mp and bp  greater polarity = higher mp and bp  greater van der Waals’ = higher mp and bp  often dissolve in nonpolar solvents but not in strong polar solvents like water  do not conduct electricity

32.  high mp and bp › decreases going down the periodic table  harder for cations to attract the sea of electrons › increases going across the periodic table  atomic radii becomes smaller, easier to attract the sea of electrons  low volatility  not soluble in most solvents (polar or non-polar)  conduct electricity well because of moving sea of electrons

34.  from highest to lowest 1. metallic bonds 2. ionic bonds (cations and anions) 4. hydrogen bonding (strong δ+ or δ-)  very strong when H is bonded with NOF (nitrogen, oxygen, or fluorine) 5. dipole - dipole *δ+ or δ-) 6. London forces (weak, temporary δ+ or δ-)

35.  generally speaking › the greater the intermolecular force (IMF) between the molecules, the higher the melting point, boiling point, and volatility (evaporate)  more electrons help increase the van der Waals’ forces and keep the substance in the liquid state  molecules that can stick together better remain a liquid at higher temps. boiling point increases this flat shape allows it to stick to one another better these round shapes do NOT allow them to stick to one another

36. hydrogen bonding can occur here which is the strongest type of dipole : dipole intermolecular force only normal dipole : dipole bonding can take place ethanol - higher BP dimethyl ether - lower BP Exampe: two Lewis structures for the formula C 2 H 6 O. Compare the boiling points of the two molecules.

37.  “like dissolves like” › polar substances tend to dissolve in polar solvents (ex. water dissolves ionic compounds)  dissociation of salt YouTube (:53) dissociation of salt YouTube (:53) › non-polar substances tend to dissolve in non-polar solvents (ex. alcohol dissolves covalent molecules)  metals do not dissolve in most solvents

39. ++ –– ++ ++ –– ++ ++ –– ++ ++ –– ++ ++ –– ++ ++ –– ++ ++ –– ++ ++ –– ++ ++ –– ++ The dipoles of water attract, pushing the oil (with no partial charge) out of the way: attractions win out over the tendency toward randomness.

40.  substances must possess Freely Moving Charged Particles › this occurs in…  metals with their “sea of electrons”  YouTube (1:05) YouTube (1:05)  molten ionic compounds (+ and – ions can move)  http://www.dynamicscience.com.au/tester/solutions/ chemistry/bonding/bonding5.htm http://www.dynamicscience.com.au/tester/solutions/ chemistry/bonding/bonding5.htm  ionic compounds in aqueous solution (dissolved in water)  water pulls apart + and – ions and allows them to move

41. Type of Bonding Melting Point Boiling Point Volatilit y Electrical Conductivity Solubility in Non- polar Solvent Solubilit y in Polar Solvent Non- polar Low HighNoYesNo Polarvaries No Yes Hydroge n bonding varies No Yes Ionic Bonding high lowYes (molten or aqueous) NoYes (most) Metallic Bonding high lowYesNo Covalentvaries No Giant Covalent High LowNo (except graphite) No