CHEM 1212 General Chemistry II Chapter 10 Liquids and Solids Spring 2023 Dr Wenjian Vince Du 1 In Ch 5 we saw that the properties of all ideal gases were the same regardless of the chemical identity of the substance The properties of liquid and solids have a dependence on the chemical identity of the substance States of Matter The fundamental difference between states of matter is the strength of the intermolecular forces of attraction Stronger forces bring molecules closer Kinetic energy keeps them apart and together moving 3 Phase Changes Between Solids Liquids and Gases Phase Change State Change A change in the physical form but not the chemical identity of a substance Fusion melting Solid to liquid Vaporization Liquid to gas Sublimation Solid to gas Freezing Liquid to solid Condensation Gas to liquid Deposition Gas to solid 4 10 1 Intermolecular Forces Intermolecular Forces IMFs The various forces of attraction that may exist between the molecules of a substance IMFs are a result of electrostatic phenomena IMFs are non covalent forces Intramolecular Forces The forces that hold atoms together within a molecule Ionic bonding Covalent bonding The differences in the properties of a solid liquid or gas are a result of differences in strengths of the IMFs that make up each substance Types of Intermolecular Interactions Forces The strength of IMFs vary for different substances All IMFs are significantly weaker than intramoleculer forces covalent bonds Three types of IMFs 1 Dispersion Forces 2 Dipole Dipole Attractions 3 Hydrogen Bonding The Intermolecular Forces above are sometimes collectively referred to as van der Waals forces Other types of IMFS Ion dipole forces ion induced dipole forces dipole induced dipole forces 6 7 Dispersion Forces All substances polar and non polar have Dispersion Forces Constant motion of electrons in molecules and atoms result in instantaneous dipoles An instantaneous dipole in one molecule or atom can then distort the electrons in a neighboring atom or molecules producing an induced dipole Both of these fleeting temporary dipoles result in weak electrostatic forces known as dispersion forces 8 London Dispersion Forces video 9 Dispersion Forces and Molar Mass number of electrons As the atomic number increases the number of electrons increases and there is a stronger dispersion force Larger molecules and atoms with more electrons exhibit stronger dispersion forces than smaller molecules and atoms with fewer electrons This is because larger atoms have greater polarizability due to the greater number of electrons in their electron clouds so they are easier to be distorted Polarizability The measure of how easy it is for another electrostatic charge ion dipole to distort a molecule s atom s electron charge distribution 10 London Dispersion Forces Melting Points and Boiling Points of the Halogens Halogen mp K 53 5 171 6 265 9 386 8 bp K 85 0 239 1 331 9 457 5 F2 Cl2 Br2 I2 As the molar mass increase the dispersion forces increase As the dispersion forces increase the intermolecular forces increase As the intermolecular forces increase the melting boiling point increases 11 Dispersion Forces and Molecular Shape The strength of the dispersion forces also increases with increasing contact area between molecules The linear isomer has greater dispersion forces Linear isomer Branched isomer Rod shape Spherical shape less compact more compact Dipole Dipole Attractions Molecules with permanent dipoles display Dipole Dipole Attractions Present only in polar molecules Dipole Dipole Attractions are usually stronger than dispersion forces Polar molecules contain both dipole dipole attractions and dispersion forces Adjacent molecules line up such that the partial negative pole of one molecule is as close as possible to the partial positive pole of another molecule 13 Dipole Dipole Forces video 14 Dipole Dipole Forces Comparison of Molecular Weights Dipole Moments and Boiling Points Substance C H 3 C H 2 C H 3 C H 3 O C H 3 C H 3 C N Molecular Wt 44 10 46 07 41 05 Dipole Moment D bp K 0 08 1 30 3 93 231 248 355 As the dipole moment increases the dipole forces increase As the dipole forces increases the intermolecular forces increase As the intermolecular forces increase the boiling point increases 15 Summary of van der Waals Forces Dispersion London forces exist between all molecules These forces increase with molecular size and depend on molecular shapes Forces associated with permanent dipoles involve displacements of electron pairs in bonds rather than molecules as a whole L D F D D H bond When comparing substances of comparable molecular sizes dipole forces can produce significant differences widely different molecular sizes dispersion forces are usually more significant than dipole forces 16 Hydrogen Bonding Hydrogen Bond An attractive force between a hydrogen atom bonded to a very electronegative atom O N or F and an unshared electron pair on another electronegative atom O N or F N H O H F H N O F 17 Hydrogen Bonding Hydrogen Bonding is the strongest van der Waals force It is a strong type of dipole dipole attraction Need a H covalently bonded to one of these highly EN elements N O or F N H O H F H N O F 18 Hydrogen Bond video 19 Hydrogen Bonding in Water Ice Liquid water Steam physical process H2 O molecules remain intact 20 Hydrogen Bonding Hydrogen bonding between guanine left and cytosine right in DNA 21 Intermolecular Forces 22 Effect of IMF s and Boiling Point 23 Other types of IMFs Ion Dipole Forces The result of electrical interactions between an ion and the partial charges on a polar molecule Cl Na 24 Other types of IMFs Ion Dipole Forces in Dissolution of a Salt 25 Other types of IMFs Ion Induced Dipole A temporary dipole that is created due to the influence of a neighboring ion Cl Spherical atom with no dipole HeHe 26 Other types of IMFs Dipole Induced Dipole A temporary dipole induced dipole that is created due to the influence of a neighboring dipole permanent dipole from a polar molecule Spherical atom with no dipole HeHe 27 Comparison of Intermolecular Forces Strength kJ mol Characteristics Highly variable 40 600 Moderate 10 40 molecules with O H N H and F ions and polar molecules H bonds polar molecules ion and nonpolar molecule polar molecule and nonpolar molecule variable 0 05 40 all molecules strength depends on size shape polarizability Force Ion dipole Hydrogen bond Dipole dipole Weak 5 25 Ion induced dipole Dipole induced dipole London