Intermolecular Forces PDF

INTERMOLECULAR FORCES  Why is water liquid at room temperature but salt (NaCl) is a solid?  Draw a picture of a solid, a liquid and a gas What happens when you heat solid water to 100°C? Why? How? What happens when you heat solid sodium chloride to 100°C? Why? How? Wha...

INTERMOLECULAR FORCES  Why is water liquid at room temperature but salt (NaCl) is a solid?  Draw a picture of a solid, a liquid and a gas What happens when you heat solid water to 100°C? Why? How? What happens when you heat solid sodium chloride to 100°C? Why? How? What happens to the bonding and structure when you heat diamond?  H H H C H H C H What happens to the bonding H H and structure when you heat H H methane? H C H H C H H H  H H H C H H C H H H H H H C H H C H H H What happens to the bonding H IH IH I and structure H IH IH I when you H IH IH I heat HI? H IH IH I  H I H I H I H I H I H I H I H I H I H I H I H I  Which are greater? Forces WITHIN individual people holding their ATOMS together Forces BETWEEN people holding them in a GROUP  Which are greater? Forces WITHIN a molecule, holding ATOMS together INTRAMOLECULAR FORCES Forces BETWEEN molecules, holding them together in a specific STATE INTERMOLECULAR FORCES  INTRAMOLECU H I Ionic LAR H I H I INTERMOLECUL H I AR Covalent polar H I London Dispersion H I Covalent H I Dipole Dipole non-polar H I H Hydrogen IBonds H I H I H I  INTERmolecular forces Between molecules Attract one molecule to another Only occurs between covalent molecules Without these forces, all molecular substances would be gases at all temperatures Enable molecules to form liquid and solid states 1) Van der Waals Forces A) London Dispersion (LD) Forces Present in ALL molecular molecules Weakest type of intermolecular force Possible for e- to concentrate in one area Creates a temporary  Strength of LD force depends on # of e- The more e- a molecule has = more LD forces Bigger = more LD forces  Strength of LD forces Order the following compounds in terms of LD forces – from Lowest to highest C3H8 C2H6 CH4 C4H10 Answer: CH4 C2H6 C3H8 C4H10  H-I H-I B) Dipole – Dipole Exist between molecules that are polar Strength of force depends on size of dipole Difference in electronegativity Stronger dipole = stronger force  DD Forces Order the following from weakest to strongest DD force: FI ClF BrCl IBr Answer: BrCl IBr ClF FI  Influence of DD Forces Br2 vs. ICl - Who is more likely to be a liquid vs gas @ RT? To be a LIQUID, molecules need to be held closer together More intermolecular forces  LD forces: # e- = ? 70 e- each Have same LD forces DD forces: ICl is polar, Br2 is non-polar ICl has DD forces ICl has more intermolecular forces More likely to be Liquid @ RT 2) Hydrogen Bonding When H is bonded to a highly electronegative atom (F, O, N) Extremely polar bond H nucleus (+) is attracted to the lone pairs of adjacent to atom Any molecule with –FH, –OH or – NH group will show H-bonding  PRACTICE WORKBOOK #12 & 13  H-BONDING CAN BE SEEN IN: PROTEIN STRUCTURE DNA DENSITY OF ICE  EFFECTS OF BONDING ON PHYSICAL PROPERTIES Melting/boiling points are a measure of the strength of intermolecular forces Ionic bonds = highest MP/BP More intermolecular forces =  in MP/BP All 3 = higher MP/BP Only LD = lower MP/BP  Put in order of low to high BP: NaCl CH3Cl CI4 H2O CH3I Answer: CI4 CH3I CH3Cl H2O NaCl  Put in order of solubility: NaCl CH3Cl CI4 CH3I Like dissolves like Soluble = like water Water = HB, DD, LD Ionic (aq) = most soluble Breaks into ions More intermolecular forces = more soluble  PRACTICE WORKBOOK #14 & 15