11 1 Intermolecular Forces Keeping Matter Together Natures

11. 1 Intermolecular Forces Keeping Matter Together Nature’s Forces 1 5. 2. 00 4: 24 PM

Phases of Matter: Terminology Energy is required for phase change to occur. Solid-Liquid-Gas Triangle 2 5. 2. 00 4: 24 PM

Heating Cooling Curve From Steam to Ice and Vice-versa 2. 09 J g° 1. 84 J g° 4. 184 J g° 0. 43 cal g° 40. 67 k. J mol 1 cal go 540 cal g How much energy of 1 g H 2 O 100°C to 0°C ? 3 0. 50 cal g° 6. 01 k. J mol 80 cal g 540+100+80=720 cal 5. 2. 00 4: 24 PM

Intermolecular Forces At the molecular level: Molecules or matter is held together by attractive force “glue” called intermolecular forces 4 Energy added (K. E. increase) 5. 2. 00 4: 24 PM

Keeping Matter together Intramolecular Forces Force which keeps integrity of molecule together, i. e. , bonds or electrostatic bonding. Intermolecular Forces Attractive force between molecules. Responsible for keeping matter in solid or liquid phase 5 5. 2. 00 4: 24 PM

The Forces be with You 2 Basic types of Intramolecular Force Ion - ion - Electrostatic attraction Covalent Bonds - Mutual sharing of electrons 4 Basic types of Intermolecular Force* 1. Ion - dipole : Ion is attracted to polar molecule 2. dipole - dipole: Polar molecules attracted to each other. 3. dipole - induce dipole: Polar molecules attracted to nonpolar molecules. 4. induce dipole -induce dipole (Van der Waal’s forces – also called London dispersion forces) nonpolar molecules attraction for each other due to electron cloud distortion. 6 * plus one 5. 2. 00 4: 24 PM

Relative Strength Interaction ion- ion Covalent Bonds ion-dipole (I-D) dipole - dipole (D-D) dipole - induce dipole (D-ID) Van der Waal 7 • H-Bond (10 - 40 k. J/mol Example Na+ Cl. H-H Na+ H 2 O ICl HCl O 2 N 2 Energy 400 -4000 k. J/mol 150 -1100 k. J/mol 40 -600 k. J/mol 5 -25 k. J/mol 2 -10 k. J/mol 0. 05 - 40 k. J/mol 5. 2. 00 4: 24 PM

Ion - Ion Covalent Bonds Ion - Ion: Electrostatic attraction between ions Bond Energy: = 926 k. J/mol Covalent Bonds: Bond between atoms as a result of electrons sharing. Bond Energy: = 159 k. J/mol 8 5. 2. 00 4: 24 PM

Ion - Dipole: Charge and size dependent. Most important for larger charge and small ionic radius. Cation Li+ Na+ K+ RB+ Cs+ 9 Ion Radius 90 116 152 166 181 DHHyd (k. J/mol) -515 -405 -321 -296 -268 5. 2. 00 4: 24 PM

Dipole - Dipole: A permanent attractive intermolecular force resulting from the interaction of the positive end of one molecule with the negative end of another. Occurs between identical or different polar molecules. Non. Polar M(g/mol) bp (°C) N 2 28 -196 Si. H 4 32 -112 Ge. H 4 77 -90 Br 2 160 59 10 Polar M (g/mol) CO 28 PH 3 34 As. H 3 78 ICl 162 bp(°C) -192 -88 -62 97 5. 2. 00 4: 24 PM

Induce dipole - induced dipole: Vander Waal’s forces Van der Waal (Induced dipole-Induced dipole): Intermolecular force responsible for keeping nonpolar molecules (species) together. Polarisability - The ease of which an e- cloud can be distorted. Larger the atomic size, the greater the number of electrons, the greater the polarizability. 11 Boiling Point of the Halogens and Noble Gases Halogen B. pt (K) Noble Gas B. pt (K) F 2 Cl 2 Br 2 I 2 He Ne Ar Kr 4. 6 27. 3 87. 5 120. 9 Xe 166. 1 85. 1 238. 6 332. 0 457. 6 5. 2. 00 4: 24 PM

Boiling point versus polarisability How about H 2 Te, (-20°C) H 2 Se, H 2 S, H 2 O 12 0°C Ge. H 4 -100°C Temperature Graphs for noble gases and for series of nonpolar molecules; both show a family smooth increase of boiling point with atomic weight (larger degree of polarisability) due to increasing Van der Waal forces Si. H 4 CH 4 -200°C He -250°C Sn. H 4 Xe Kr Ar Ne Molar Mass 5. 2. 00 4: 24 PM

Boiling point Hydrogen compounds 100°C H 2 O HF NH 3 H 2 S Temperature Graphs for family of hydrogen containing compounds and their boiling point. In general there is an increase in the boiling point except for H 2 O, HF and NH 3. Why? There must be some other force that operate on these compounds which increases their intermolecular forces. HCl PH 3 Si. H 4 -100°C H 2 Te Sb. H 3 HI H 2 Se As. H 3 HBr Sn. H 4 Ge. G 4 CH 4 Molar Mass (Period) 13 5. 2. 00 4: 24 PM

A Special Type of Bonding H-Bonding: A special glue above and beyond dipole intermolecular forces. H-bonding is a strong type of intermolecular force (bond) between hydrogen and very electronegative elements ( 4 - 30 k. J/mol). N-H O-H F-H sometimes (Cl-H) Bichemical structural Integrity. Water possesses H-bond: Responsible for water’s unique properties. 14 5. 2. 00 4: 24 PM

Example: H-bonding Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate. a) C 2 H 6 d) H 3 CCOOH No Yes b) CH 3 OH e) H 3 CCH 2 OH Yes c) H 3 CCONH 2 Yes 15 Yes f) H 3 CCOCH 3 No 5. 2. 00 4: 24 PM

Biological Integrity H-bonding is responsible for the structural integrity of Biological molecules. • Protein structures 16 • DNA and RNA 5. 2. 00 4: 24 PM

H 2 O: Nature of Water is a liquid at room temperature as a direct consequence of hydrogen bonding between adjacent water molecules. (Most other molecules with comparable Molar mass is a gas at room temperature) Pure water is a liquid between 0°C and 100°C. 17 5. 2. 00 4: 24 PM

Example Identify the dominant intermolecular forces for each of the following substances, and select the substance with the higher boiling point in each pair; a) Mg. Cl 2 or PCl 3 ion-dipole Vd. W Higher Bpt b) H 3 CNH 2 or CH 3 F dipole-dipole Vd. W Higher Bpt b) CH 3 OH or CH 3 CH 2 OH dipole-dipole e) Hexane or cyclohexane H-bond Vd. W dipole-dipole Vd. W More surface area Higher Bpt Higher MWt. 18 H-bond Vd. W Higher Bpt 5. 2. 00 4: 24 PM

Overview: Recognizing Intermolecular Forces Flowchart for recognizing the major types of intermolecular forces. Van der Waal’s forces occur in all instances. The strength of other forces generally increases proceeding from left to right 19 5. 2. 00 4: 24 PM

Summary of Nature’s Forces Bonding forces are relatively strong because they involve larger charges that are closer together. Ionic (4004000 k. J/mol) Metallic (75 -1000 k. J/mol) Intermolecular forces are relatively weak because they typically involve smaller charges that are farther apart. H-bond (10 -40 k. J/mol) LDF (0. 05 - 40 k. J/mol) 20 5. 2. 00 4: 24 PM