Chapter 11 Lecture 1 and 2: Liquids, Solids, and Intermolecular Forces, Lecture Notes

Chapter 11 Lecture 1 and 2 Liquids, Solids, and Intermolecular Forces  Phases of Matter https://myarkansaspbs.pbslearningmedia.org/resource/phases-of-matter-the-3-phases-animation/unc-tv-science/ Properties of the States of Matter: Solids High densities compare...

Chapter 11 Lecture 1 and 2 Liquids, Solids, and Intermolecular Forces  Phases of Matter https://myarkansaspbs.pbslearningmedia.org/resource/phases-of-matter-the-3-phases-animation/unc-tv-science/ Properties of the States of Matter: Solids High densities compared to gases. Nonfluid. They move as an entire “block” rather than a smooth, continuous flow. Keep their own shape, do not take the shape of their container(s). Keep their own volume, do not expand to fill their container(s). Cannot be compressed into a smaller volume. 3 Properties of the States of Matter: Liquids High densities compared to gases. Fluid. The material exhibits a smooth, continuous flow as it moves. Take the shape of their container(s). Keep their volume, do not expand to fill their container(s). Cannot be compressed into a smaller volume. 4 Properties of the States of Matter: Gases Low densities compared to solids and liquids. Fluid. The material exhibits a smooth, continuous flow as it moves. Take the shape of their container(s). Expand to fill their container(s). Can be compressed into a smaller volume. 5 The state which occurs will depend on two things: 1. The kinetic energy in the particles (proportional to temperature) 2. The strength of the forces binding the particles together. Changes Between States Example of Change Between States Liquefied petroleum (LP) gas used as a fuel for outdoor grills and lanterns. Gas at room temperature and atmospheric pressure. Liquid at 2.7 atm. Intramolecular vs Intermolecular Forces Intramolecular forces are interactions of atoms within a molecule. Intermolecular forces are interactions between molecules. Among other things, intermolecular forces are responsible for condensation of gases, and freezing of liquids into solids. Intermolecular Forces Attractive Forces Intermolecular forces (IMF): electrostatic Strength varies, dependent on structure and charge. The stronger the attractive forces between the particles, the more they resist moving though no material completely lacks particle motion Intermolecular Forces (also called non-covalent interactions) Attractive forces between molecules and ions. Determine bulk properties of matter. Much weaker than chemical bonds. (10’s of kJ/mol vs. 100’s of kJ/mol) (this is why boiling water doesn’t make hydrogen and oxygen, just make steam.) Think of as the “stickiness” of the particles Several types, dependent on structure and charge distribution.  Coulomb’s Law 1  q1q2  the potential energy (E) of two oppositely charged particles (with E   charges q1 and q2) decreases (becomes more negative) with increasing magnitude of charge and with decreasing separation k r  (r). k is constant equal to 4πϵ˚. But we know that molecules can have partial charges if they have polar bonds. The interactions between these partial charges are the basis of intermolecular forces. δ- δ+ δ- δ+ Intermolecular Forces  1  q1q2  E   k r  What does this tell you about the strength of intermolecular forces compared to bonding forces ? Intermolecular forces also act over much larger distances compared to electron-proton interactions. Intermolecular Forces Several types of forces: Dispersion instantaneous induced dipole all molecules/atoms/ions experience this interaction Strength depends on polarizability of particle Dipole-Dipole molecule must have a permanent dipole depends on dipole moment Hydrogen Bonding must be a polar molecule H covalently-bound to F, N, or O Ion-Dipole Interactions between ions and polar molecules Dispersion Forces Attraction is due to instantaneous, temporary dipoles formed due to electron motions. Temporary partial charges Instantaneous Dipoles 17 All molecules, regardless of structure, experience dispersion forces. These include nonpolar molecules. -Now suppose that one of the molecules has, for a split second, an unsymmetrical distribution of charge. -The existence of this temporary dipole induces dipole moments in adjacent molecule. The magnitude of the dispersion force depends on the polarizability and shape of the atom or molecule.  volume of the electron cloud  larger molar mass = more electrons = larger electron cloud = increased polarizability = stronger attractions  more surface-to-surface contact = larger induced dipole = stronger attraction Effect of Molar Mass on Boiling Points Effect of Molecular Shape on Size of Dispersion Force the larger surface-to- surface contact between molecules in n-pentane results in stronger dispersion force attractions Practice – Choose the Substance in Each Pair with the Higher Boiling Point a- Both a) CH4 C4H10 molecules are nonpolar larger molar mass b) C6H12 C6H12 b- Both molecules are nonpolar, but the flatter ring molecule has larger surface- to-surface contact Dipole–Dipole Attractions Polar molecules have a permanent dipole because of bond polarity and shape dipole moment as well as the always present induced dipole The permanent dipole adds to the attractive forces between the molecules raising the boiling and melting points relative to nonpolar molecules of similar size and shape Molecular Polarity  Dipole-Dipole Attractions Strength of the interaction depends on the magnitude of the dipole. Indicates similar polarizabilities, therefore similar dispersion effects. Practice – Choose the substance in each pair with the higher boiling point a) CH2FCH2F CH3CHF2 or b) or Practice – Choose the substance in each pair with the higher boiling point a) CH2FCH2F CH3CHF2 more polar b) or polar nonpolar Hydrogen-Bonding Molecules containing N–H, O–H, or F–H groups, and an electronegative O, N, or F. Not really a chemical bond! Can vary from ~10 to ~100 kJ/mol. H-Bonding in Water Hydrogen bonding DNA Double Stranded DNA Practice – Choose the substance in each pair that is a liquid at room temperature (the other is a gas) a) CH3OH CH3CHF2 can H-bond b) CH3-O-CH2CH3 CH3CH2CH2NH2 can H-bond  Ion–Dipole Attraction In a mixture, ions from an ionic compound are attracted to the dipole of polar molecules The strength of the ion–dipole attraction is one of the main factors that determines the solubility of ionic compounds in water  IMF and Solubility Solubility depends, in part, on IMF like dissolves like Polar substances dissolve in polar solvents hydrophilic groups = OH, CHO, C=O, COOH, NH2, Cl HO H OH H O O H N H HO H C C H C O H H O H H HO OH Acetic Acid Ammonia Methanol Ascorbic Acid (Vit. C) Nonpolar molecules dissolve in nonpolar solvents; Hexane, Pentane hydrophobic groups = C-H, C-C Immiscible Liquids Pentane, C5H12 is a nonpolar molecule. Water is a polar molecule. The attractive forces between the water molecules is much stronger than their attractions for the pentane molecules. The result is the liquids are immiscible. Polar Solvents Ethanol (ethyl alcohol) Dichloromethane Water (methylene chloride) Nonpolar Solvents Practice – Choose the substance in each pair that is more soluble in water a) CH3OH CH3CF2 H can H-bond with H2O more polar b) CH3CH2CH2CH2CH3 CH3Cl