Class Notes (837,426)
Canada (510,272)
Chemistry (543)
CHEM 1AA3 (67)
Lecture

CHEM 1AA3 - Intermolecular Forces Chapter 12.docx

34 Pages
96 Views
Unlock Document

Department
Chemistry
Course
CHEM 1AA3
Professor
Jeff Landry
Semester
Fall

Description
CHEM 1AA3: Intro. Chemistry II Ch.12: Liquids, Solids & Intermolecular Forces Chapter 12 • Exclude: sections 12.7-12.9 • Include: sections 12.1(only capillary action),12.2-12.6 (much of which was discussed in Chem 1A03 – recall: properties of water) • Intermolecular Forces = IMF 2 22 Chem 1AA3 12.5 & 12.6: Intermolecular Forces In pure substances: • van der Waals forces • Dipole-dipole forces • Hydrogen-bonding forces In solutions we also see: • Ion-dipole forces • Ionic interactions e.g., iodine e.g., acetone e.g., water e.g., hydrated ions e.g., hydrated ions 3 33 Chem 1AA3 12.5: van der Waals forces 4 44 Chem 1AA3 • Also called induced dipole-induced dipole forces or London dispersion forces (a) nonpolar molecule, (b) experiences an instantaneous dipole, (c) which induces a dipole in its neighbour. • Instantaneous dipoles propagate throughout the sample • Force strength depends on polarizability (the tendencyfor charge separation to occur). Fig. 12-24, p. 490 12.5: van der Waals forces 5 55 Chem 1AA3 • van der Waals forces increases with: -atomic number and size of the molecule (due to polarizability) -linear versus branched structures (due to increased intermolecular contact area) Fig. 12-25 Pentane, b.p. = 36.1 °C Neopentane, b.p. = 9.5 °C Table 9-5 (p. 359) Molecule Melting point Cl2 172 K I2 387 K 12.5: Dipole-dipole forces 6 66 Chem 1AA3 • Occur in polar molecules (molecules with permanent dipoles) – polar molecules have bond dipoles and asymmetric shape • Being polar increases b.p. over dispersion forces alone – e.g., N2 (77K), NO (121 K), O2 (90 K) Fig. 12-26 e.g., acetone p. 491 77Chem 1AA3 12.6: Hydrogen bonding • Between an H atom in a polar bond (i.e., H-N, H-O, or H-F) and another electronegative atom (i.e., N, O, or F) • One H-bond is small, but many are mighty. p. 495 N N N N N NN O O N N N O N N N NO N dR dR dRdR HH H H H H H H cytosine(C) guanine(G) thymine(T) adenine (A) = hydrogen bond dR = deoxyribose Base-pairing in DNA N H HHN H H H d-d+ Base-pairing in ammonia 77Chem 1AA3 12.6: Hydrogen bonding • Between an H atom in a polar bond (i.e., H-N, H-O, or H-F) and another electronegative atom (i.e., N, O, or F) • One H-bond is small, but many are mighty. p. 495 N N N N N NN O O N N N O N N N NO N dR dR dRdR HH H H H H H H cytosine(C) guanine(G) thymine(T) adenine (A) = hydrogen bond dR = deoxyribose Base-pairing in DNA N H HHN H H H d-d+ Base-pairing in ammonia Effects of Hydrogen bonding Fig. 12-27 8 88 Chem 1AA3 How mighty are those H-bonds? • Demonstration: 2 magazines with pages interwoven • Mythbusters video of phone books: http://www.wimp.com/themyth/ • They are very mighty! (8000 lb force to separate the phone books) 9 99 Chem 1AA3 Ionic Interactions Chem 1AA3 • Ionic interactions are very favourable in solids, but are weaker in solution, and can even be unfavourable in water, where solvation of the individual ions by water can be more favourable than the ionic interactions http://www.ck12.org/flexr/chapter/2325/ & JLM Visuals Melting point = 801 °C Solid NaCl Na+ Cl-H O H H H O H O H H O H H O HH O H H O H O H H H O H H H O H O H Aqueous NaCl solution 10 1010 1111Chem 1AA3 Ionic Interactions Immuno-isolation shells for islets of Langerhans Polymer shells composed of 9 alternating polyanion/ polycation layers are used to encapsulate islets of Langerhans for transplantation into diabetics' pancreas. They can then produce insulin, but are protected from immune system rejection. Layer-by-layer polyelectrolyte deposition 1111Chem 1AA3 Ionic Interactions Immuno-isolation shells for islets of Langerhans Polymer shells composed of 9 alternating polyanion/ polycation layers are used to encapsulate islets of Langerhans for transplantation into diabetics' pancreas. They can then produce insulin, but are protected from immune system rejection. Layer-by-layer polyelectrolyte deposition Relative Strengths of IMFs: A summary 12 1212 Chem 1AA3 • All molecules have van der Waals forces • The range of strength for each force type overlaps, but approximately: van der Waals < Dipole < H-bonding < Ionic/Covalent *values from p. 451, Chemistry, Silberberg, 5th ed. and other sources -350 (per bond)C-C covalent bond 4 to -760Ionic -15 to -40 (per bond)Hydrogen bonding -5 to -25Dipole ~ -0.05 (per atom)van der Waals Interaction energy (kJ/mol)*Interaction 12.2/12.6: Liquids 13 1313 Chem 1AA3 • Impact of IMF strength: p. 496 e.g., more H-bonding = higher viscosity (measured in cP, centipoise) Ethanol Ethylene glycol Glycerol 1.2 cP 20 cP 1500 cP increasesViscosity increasesMelting Point (m.p.) decreasesVapour pressure increasesBoiling point (b.p.) Effect of increasing IMFPhysical property PH Formative iClicker Question #16 14 1414 Chem
More Less

Related notes for CHEM 1AA3

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit