CHAPTER 10 TERMS Alloy: a substance that contains a mixture of elements and has metallic properties Dipole-dipole attraction: the attractive force resulting when polar molecules line up so that the positive and negative ends are aligned between molecules Enthalpy of fusion H fus : enthalpy change that occurs at the melting point when a solid melts. Enthalpy of vaporization, H vap : the energy required to vaporize 1 mole of a liquid at a pressure of 1 atm. Also called the enthalpy of vaporization. Equilibrium: the point at which further net change occurs in the amount of liquid or vapor because the rate of evaporation and condensation are the same. Equilibrium vapor pressure (vapor pressure): the pressure of the vapor present at equilibrium. P atmosphere = P vapor + P Hg column Hydrogen bonding: Intermolecular forces: Ionic IMF: an attraction between an H-atom covalently bonded to an F, O or N-atom in a molecule and the lone pair electrons on a (different0 F, O or N-atom (hydrogen FONdling) relatively weak attractive interactions that occur between molecules Force of attraction found in ionic compounds due the attraction of oppositely charge ions. London dispersion forces: an attraction that occurs between two atoms when the electrons in one are temporarily unevenly distributed resulting in a momentary dipole across the atom. This dipole induces similar distributions in neighboring atoms which causes an attractive force. Metallic IMF: Network Covalent IMF: Phase diagram: Ranges of motion: Semiconductor: Vapor Pressure: Force of attraction found in metals due to the delocalization of electrons. Solid containing strong directional covalent bonds. Ex: SiO 2 (sand), C(diam) and C (graph) represents the phases of a substance as a function of temperature and pressure. Triple point- when the solid and liquid states of water have identical vapor pressures. Critical temperature- temperature above which the vapor cant be liquefied matter what pressure is applied. Critical pressure- pressure required to produce liquefaction at the critical temperature. Critical point- both the critical pressure and temperature. solid vibrational motion liquid vibrational and rotational motion gas vibrational, rotational and translational motion a substance conducting only a slight electrical current at room temperature, but showing increased conductivity at higher temperatures The pressure exerted by the vapor phase of a substance above the liquid phase. As the temperature of the liquid increases, more vapor is created so that vapor pressure increases with temperature. Vapor pressure is highest as the temperature nears the boiling point. Boiling will occur when the vapor pressure matches atmospheric pressure. Vaporization/evaporation: molecules gain eugh energy to move from liquid to vapor The Liquid State characteristics: low compressibility, lack of rigidity, and high density (compared with gases) surface tension: the resistance of a liquid to an increase in its surface area liquids with relatively large intermolecular forces, such as those with polar molecules, tend to have relatively high surface tensions capillary action: the spontaneous rising of a liquid in a narrow tube two different types of forces are responsible for this property: 1) cohesive forces: the intermolecular forces among the molecules of the liquid 2) adhesive forces: the forces between the liquid molecules and their container
CHAPTER 10 CONCEPTS Phase Change and IMF CHAPTER 10: LIQUIDS AND SOLIDS For a substance to change phase (s l g) eugh energy must be added to overcome the intermolecular force, IMF. The stronger the IMF then the more energy that must be added, so that stronger IMF s result in higher melting/boiling points while a substance with a weaker IMF would have a lower melting/boiling point. Thus, a substance s IMF and melting/boiling point are directly related. Also, a substance can have more than one IMF, but usually only the strongest IMF is needed to asses which of a group of substances would have a higher/lower melting or boiling point. More on Some Intermolecular Forces, IMF s (brief explanations may be found in the list of terms) Note: intramolecular within the molecule chemical bonds Intermolecular between molecules IMF s I. Dipole-Dipole IMF dipole moment: a property of a molecule whose charge distribution can be represented by a center of charge and a center of negative charge positive A dipole is created in a polar bond due to the unequal sharing of electrons. Within the bond, the more electronegative atom becomes partially negative, while the less electronegative atom becomes partially positive. The dipole-dipole force of attraction is a result of the dipole in one molecule being attracted to the dipole in ather molecule resulting in an array of dipole with opposite ends near one ather. dipole-dipole forces are typically only about 1% as strong as covalent or ionic bonds II. Hydrogen BondingIMF hydrogen bonding: unusually strong dipole-dipole attraction that occur among molecules in which a hydrogen that is bonded to an N, O or F atom is attracted to the lone pair electrons on ather N, O or F atom two factors account for the strengths of these interactions: 1) the great polarity of the bond 2) the close approach of the dipoles, allowed by the very small size of the hydrogen atom III. London Dispersion IMF London dispersion forces: these are weak forces that exist in all atoms. The force is due to the temporary formation of a dipole that results from the majority of the electrons being located on one side of the atom creating a partial negative charge while the other side of the atom becomes partially positive due to the increased exposure of the nucleus. This temporary dipole induces neighboring atoms to do the same. LD forces are the only and thus primary IMF among singular atoms and npolar molecules. London dispersion forces increase with the size of an atom or molecule due to the larger dipole that is created with an increased number of electrons and protons. Thus, larger singular atoms and npolar molecules will have a higher melting/boiling point; for example see the halogen family. IV. Table Relating the Strengths of IMF's to a Low or High Melting/Boiling Point Melting/Boiling Point IMF Strength Types of IMF (with a hint on how to identify the IMF) lowest weakest London Dispersion (npolar molecules) Dipole-Dipole (polar molecules, HO, HN, HF bonds) Hydrogen Bonding (polar molecules, with HO, HN, HF bonds) highest strongest Network Covalent, Ionic, Metallic
Determining IMF from Chemical Formulas To determine the intermolecular force (IMF) of a substance, follow the arrows when answering the following sequence of questions. Each path ends at a bold-printed IMF. Once you arrive at a bold-printed IMF you have identified the IMF for your substance. What types of atoms are in your substance? No metal atoms Only metal atoms Metal with nmetal Metallic Ionic is the molecule - SiO 2, graphite or diamond? Network Covalent Identifying Phase Change are the nmetals only C, H, P, As, S and/or Se? (nmetals with similar electronegativities) London Dispersion is there at least one -HO, HN or HF- bond? Hydrogen Bonding Dipole-Dipole A substance undergoes a phase change when the temperature (and pressure) corresponds to the melting/ boiling point temperature. At this point the temperature remains constant until the phase change is completed. A substance undergoes heating/cooling (use specific heat) at any other temperature(s). Note that temperature change is T = T f T i. Calculating the energy of a phase change 1 st Identify when the substance is undergoing a phase change (temperature is constant), and when the substance is heating/cooling (temperature is changing). 2 nd Calculate the heat released or absorbed. phase change q = n( H fus or vap ) or q = m( H fus or vap ) - use moles or mass depending on what the units are for the H (J/mol or J/g) heating/cooling q = m T C p 3 rd Add the heats,(q's) for each step. 4 th For more advanced problems, you will then compare this amount of heat to the amount of heat needed for a second process with the goal being to determine if eugh heat is available for that second process to occur. ex Calculate the heat needed to heat a 50.0 g sample of water from -10.0 C to 115.0 C. q = q 1 + q 2 + q 3 + q 4 + q 5 q = q -10 0 + q melt + q 0 100 + q boil + q 100 110 q = m TC p + n ( H fus ) + m TC p + n ( H vap ) + m TC p
Labeling phase diagrams: Be able to identify: areas of phases (solid, liquid, gas) areas of phase change (boundary lines) melting point or boiling point at a specific temperature triple point, critical point, critical pressure.
Name: AP Chemistry Period: Date: R.F. Mandes, PhD, NBCT Complete each table with the appropriate information. Compound IMF 1 CH 4 2 H 2 O 3 Cl 2 4 K 3 PO 4 5 CH 3 CH 2 OH 6 CH 3 OCH 3 7 CH 3 (CH 2 ) 3 CH 3 8 HF 9 H 2 NCH 2 CH 3 10 Cl 3 CCH 2 CH 3 11 C (graph) 12 CO 2 Compounds IMF for each compound Rank IMF (weak strong) Rank B. Pt. (low high) 13 Cl 2 I 2 14 NaCl HCl 15 CH 3 CN CH 3 CH 2 NH 2 16 HF HCl 17 CH 3 OH, CH 3 CH 3