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12.01 Intermolecular Forces Keeping Matter Together 12.01 Intermolecular Forces Keeping Matter Together Water crystal Nature’s Forces and the Magic of Water Dr. Fred Omega Garces Chemistry 152 Miramar College 1 Liquids and Solids and IMF 05.2015 Phases of Matter: Terminology Energy is required for phase changes to occur. Solid-Liquid-Gas Triangle 2 Liquids and Solids and IMF 05.2015 Heating Cooling Curve From Ice to Steam and Vice-versa Stage1 Stage2 Stage3 Stage4 Stage5 2.08 J 40.7 kJ g ° mol 6.01 kJ 0.43 cal mol g ° 2.05 J 80 cal g ° g 540 cal 0.49 cal 4.184 J g ° g g ° 1 cal g o Heat Addition What is the energy needed to take 1g H2O at 0°C to 100°C ? 80 +100+ 540 =720cal 3 Liquids and Solids and IMF 05.2015 Intermolecular Forces At the molecular level: Molecules or matter is held together by “glue” called intermolecular forces SOLID LIQUID GAS Energy added (K.E. increases) 4 Liquids and Solids and IMF 05.2015 Keeping Matter together Intramolecular Forces - Force which keeps molecule together, i.e., bonds. Intermolecular Forces - Attractive force between molecules. Responsible for keeping matter in solid or liquid phase. 5 Liquids and Solids and IMF 05.2015 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 (NaCl in water) 2. dipole - dipole: Polar molecules attracted to each other. 3. dipole - induce dipole: Polar molecules attracted to nonpolar molecules. (Oxygen in water) 4. induce dipole -induce dipole (London dispersion forces, LDF) nonpolar molecules attraction for each other due to electron distortion. * plus one 6 Liquids and Solids and IMF 05.2015 Relative Strength Interaction Example Energy ion- ion Na+ Cl- 400 - 4000 kJ Covalent Bonds H - H 150-1100 kJ + ion-dipole (I-D) Na H2O 40-600 kJ dipole - dipole (D-D) HCl HCl 5-25 kJ dipole - induce dipole (D-ID) H2O O2 2-10 kJ London Dispersion (LD) N2 N2 0.05 - 40 kJ • H-Bond (10- 40 kJ/mol 7 Liquids and Solids and IMF 05.2015 Property of Matter and IMF IMF manifestation on the Property of matter Boiling point – Temp. necessary to cause vapor pressure of liquid to equal 1 atm. Melting point – Temperature necessary to cause solid to change to liquid. Heats of Vaporization – Energy necessary to convert liquid to vapor Heats of Fusion- Energy necessary to melt a solid Specific Heat- Energy necessary to raise temperature one degree Heat Capacity- Energy necessary to raise 1 gram substance one degree temperature Surface tension – The force necessary to separate substances at the surface Capillary action – The interaction between adhesive force versus cohesive force Viscosity – The resistance for substance to flow Vapor pressure – The pressure substance exert in a close container. 8 Liquids and Solids and IMF 05.2015 Ion - Ion Covalent Bonds Ion - Ion: Electrostatic attraction between ions Na Na+ 11 p 11 p 12 n 12 n 11 p 9 p 12 n 10 n F F- 9 p 9 p 10 n 10 n NaF Bond Energy: = 910 kJ/mol Covalent Bonds: Bond between atoms as a result of electrons sharing. F F F2 Bond Energy: = 155 kJ/mol 9 p 9 p 9 p 9 p 10 n 10 n 10 n 10 n 9 Liquids and Solids and IMF 05.2015 Review of Polarity The Charge distribution may cancel out (nonpolar) or there may be a net distortion (polar) Analogy: 1. No one wins: nonpolar 2. One team wins: polar 3. a) no one wins: nonpolar b) one team wins: polar c) two team wins polar 10 Liquids and Solids and IMF 05.2015 Ion - Dipole Ion - Dipole: Charge and size dependent. Most important for larger charge and small ionic radius. Cation Ion Enthalpy of Hydration + (pm) (KJ/mol) - δ δ Li+ 90 -515 Na+ 116 -405 K+ 152 -321 Distance between ion center and negative pole of Rb+ 166 -296 dipole Cs+ 181 -263 11 Liquids and Solids and IMF 05.2015 Dipole - Dipole 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. NonPolar Polar M(g/mol) bp (°C) M (g/mol) bp (°C) N2 28 -196 CO 28 -192 SiH4 32 -112 PH3 34 -88 GeH4 77 -90 AsH3 78 -62 Br2 160 59 ICl 162 97 12 Liquids and Solids and IMF 05.2015 Induce dipole - induced dipole: London Dispersion Forces London Dispersion Force (Induce dipole-Induce dipole): Intermolecular force responsible for keeping nonpolar molecules (species) together. Polarizability - The ease of which an e- cloud can be distorted. Larger the atomic size, the greater the number of electrons, the greater the polarizability. Boiling Point of the Halogens and Noble Gases Halogen B.pt (K) Noble Gas B.pt (K) F2 85.1 He 4.6 Cl2 238.6 Ne 27.3 Br2 332.0 Ar 87.5 I2 457.6 Kr 120.9 Xe 166.1 13 Liquids and Solids and IMF 05.2015 Boiling point versus polarizability Graphs for family of chemicals that are polar and nonpolar; both show a fairly smooth increase of boiling point with atomic weight (larger degree of polarizability) due to increasing London Dispersion Forces 14 Liquids and Solids and IMF 05.2015 H2O: Nature of Water Water is a liquid at room temperature as 100°C H2O a direct consequence of hydrogen bonding between adjacent HF 0°C water molecules. H2Te NH (Most other molecules with 3 SbH3 H Se comparable molar mass are 2 HI H S 2 AsH gas at room temperature) 3 SnH4 -100°C HCl HBr PH Pure water is a 3 GeG4 liquid between 0°C SiH4 and 100°C. Temperature CH4 Molar Mass (Period) 15 Liquids and Solids and IMF 05.2015 A Special Type of Bonding H-Bonding H-Bonding: A special glue above and beyond dipole- dipole intermolecular forces. H-bonding is a strong type of intermolecular force (bond) between hydrogen and very electronegative elements (10 - 40 kJ/mol). N-H O-H F-H also consider chlorine (Cl-H) Biochemical structural Integrity. Water possesses H-bond: Responsible for water’s unique properties. 16 Liquids and Solids and IMF 05.2015 Biological Integrity H-bonding is responsible for the structural integrity of Biological molecules. • Protein structures • DNA and RNA 17 Liquids and Solids and IMF 05.2015 Determining IMF at Work The IMF present for matter will depend on the identity of the chemical present. For polar chemicals, dipole-dipole interaction exist as well as LDF. Dipole-dipole is the dominant IMF for polar chemicals however. For polar chemical in which H is bonded to F, N, O and Cl then in addition to the above mentioned IMF, H- bonding, the dominant IMF, is also present. For nonpolar chemicals, then LDF is the only force present. The magnitude of the IMF depends on the polarizability (LDF), dipole moment (dipole-dipole), number of H-X (H-bonding). 18 Liquids and Solids and IMF 05.2015 Example: H-bonding Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate. a) C2H6 e) H3CCOOH b) CH3OH f) H3CCH2OH c) H3CCONH2 g) H3CCOCH3 d) H3C-CF3 h) H2C=O 19 Liquids and Solids and IMF 05.2015 Example: H-bonding Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate. a) C2H6 e) H3CCOOH No Yes b) CH3OH f) H3CCH2OH Yes Yes c) H3CCONH2 g) H3CCOCH3 Yes No d) H3C-CF3 h) H2C=O No No 20 Liquids and Solids and IMF 05.2015 Example: IMF Determine type of IM forces Molecule LDF Dipole- H-bonding Polar or Dipole nonpolar C2H6 X NP CH3OH X X X P CH3F X X P H3C-O-CH3 X X P NH3 X X X P F3C-NF3 X X P 21 Liquids and Solids and IMF 05.2015 Example Identify the dominant intermolecular forces for each of the following substances, select the dominant IMF and select the substance with the higher boiling point in each pair; a) MgCl2 or PCl3 b) H3CNH2 or CH3F ion-dipole dipole-dipole H-bond dipole-dipole LDF LDF dipole-dipole LDF Higher Bpt LDF Higher Bpt c) CH3OH or CH3CH2OH e) Hexane or cyclohexane H-bond H-bond LDF LDF dipole-dipole dipole-dipole Higher Bpt LDF LDF More surface area Higher Bpt Higher MWt. 22 Liquids and Solids and IMF 05.2015 Example Identify the dominant intermolecular forces for each of the following substances, select the dominant IMF and select the substance with the higher boiling point in each pair; a) MgCl2 or PCl3 b) H3CNH2 or CH3F ion-ion dipole-dipole H-bond dipole-dipole ion-dipole LDF dipole-dipole LDF LDF LDF Higher Bpt Higher Bpt c) CH3OH or CH3CH2OH e) Hexane or cyclohexane H-bond H-bond LDF LDF dipole-dipole dipole-dipole More surface area LDF LDF (More polariable) Higher Bpt Higher MWt. Higher BPt 23 Liquids and Solids and IMF 05.2015 Summary of Nature’s Forces Bonding forces are relatively strong because they involve larger charges that are closer together. Ionic (400-4000 kJ/mol) Covalent (150-1100 kJ/mol) Intermolecular forces are relatively weak because they typically involve smaller charges that are farther apart. H-bond (10-40 kJ/ mol) LDF (0.05 - 40 kJ/mol) 24 Liquids and Solids and IMF 05.2015 Overview: Recognizing Intermolecular Forces (IMF) Flowchart for recognizing the major types of intermolecular forces.
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