To Do… Electronic homework (Lon-Capa) HW8 Type 1: due Wed., April 30 by 7 pm Exam 3 review: due Wed., April 30 by 7pm Review Sessions Tuesday: 161 Noyes Lab; 6:00-7:50 pm Wednesday: 161 Noyes Lab; 8:00-9:20 pm Exam #3: Thursday, May 1, 7 pm 114 David Kinley Hall

Intermolecular Forces (IMFs) 2

London Dispersion Forces 3

London dispersion forces All molecules exhibit these forces. Due to temporary and induced dipoles. Strongest IMFs for non-polar molecules Examples include nitrogen (N 2 ) and methane (CH 4 ). With more electrons, more chance of an induced dipole. 4

Dipole-dipole interactions 5

Polar molecules exhibit these forces. (also exhibit LDFs) Due to permanent dipoles. Stronger IMFs than LDFs (given similar sized molecules). Some polar molecules (such as H 2 O) exhibit a special kind of dipole-dipole interaction. 6

Water is a Liquid! 7

Hydrogen Bonding in Water 8

Clicker Question How many of the following interactions does CH 3 CH 2 CH 3 exhibit? London dispersion dipole-dipole hydrogen bonding A) 0 B) 1 C) 2 D)3

Clicker Question How many of the following interactions does CH 3 CH 2 OH exhibit? London dispersion dipole-dipole hydrogen bonding A) 0 B) 1 C) 2 D)3

Clicker Question How many of the following interactions does CH 3 OCH 3 exhibit? London dispersion dipole-dipole hydrogen bonding A) 0 B) 1 C) 2 D)3

Clicker Question How do you think the molecules rank with respect to boiling point? A) CH 3 CH 2 CH 3 > CH 3 OCH 3 > CH 3 CH 2 OH B) CH 3 CH 2 CH 3 > CH 3 CH 2 OH > CH 3 OCH 3 C) CH 3 CH 2 OH > CH 3 CH 2 CH 3 > CH 3 OCH 3 D) CH 3 CH 2 OH > CH 3 OCH 3 > CH 3 CH 2 CH 3 12

Ion-ion interactions Ionic compounds exhibit these forces. Due to ions. Strongest of the IMFs (given similar sized molecules). Example includes sodium chloride (NaCl). 13

Clicker Question Which of the following molecules exhibits dipole-dipole interactions? a) OF 2 b)SF 6 c)XeF 4 d)C 2 H 2 e) At least two of the above molecules (a-d) exhibit dipole-dipole interactions. 14

Clicker Question Which of the following molecules would be expected to have the lowest boiling point? a) C 4 H 10 b) NH 3 c) H 2 O d) C 2 H 6 15

Clicker Question Methane (CH 4 ) is a gas, but carbon tetrachloride (CCl 4 ) is a liquid at room conditions. Which of the following explains this phenomenon? a) CCl 4 is a polar molecule and CH 4 is not. b)CCl 4 and CH 4 have different geometries and shapes. c)CH 4 exhibits hydrogen bonding and CCl 4 does not. d)Cl is more electronegative than H. e) None of the above explanations explains this. 16

Clicker Question Which of the following molecules would be expected to have the highest melting point? a) CO 2 b)N 2 c)SO 2 d)H 2 e) H 2 O 17