Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 5. (19)-Chemical Bonds Today’s Outline..Review of shapes of molecules..Review of polarity of molecules..States of matter, solid, liquid, and gaseous states..Intermolecular forces Dipole forces Hydrogen bond Dispersion forces Forces in solution

Chapter 5. (L19)-Chemical Bonds Building Your Chemical Vocabulary Methyl mercury: CH 3 Hg +, highly toxic Dimethyl mercury: (CH 3 ) 2 Hg, extremely toxic

Chapter 5. (L19)-Chemical Bonds Review of shape of molecules..Common shapes of molecules: Molecular ShapeGeometryBond Angle Linear 1-D180º Bent 2-D<180º Triangular 2-D120º Pyramidal 3-Dvarious Tetrahedral 3-D109.5º

Chapter 5. (L19)-Chemical Bonds Review of polarity of molecules..Polarity occurs to the molecules of different kinds of atoms..Polarity occurs to the molecules of asymmetrical shape in which its polarity cannot be cancelled out...Polarity means a certain atom has more positive or negative charge locally, while the others have negative or positive charge locally, although the whole molecule has no overall net charge.

Chapter 5. (L19)-Chemical Bonds From bonding between atoms to form molecules to bonding or connection between molecules to form bulk matter..Bonding between atoms: Electrostatic attraction and sharing electrons Bonding between molecules: Intermolecular forces

Chapter 5. (L19)-Chemical Bonds States of matter: A review..Three physical states of matter: Gas, liquid, and solid..The gaseous state: Like a soccer field molecules are separated by large distances with random diffusive movement, essentially no interactions between molecules

Chapter 5. (L19)-Chemical Bonds States of matter..Three physical states of matter: Gas, liquid, and solid..The liquid state: Like a ball room molecules are in close contact, but loosely, free to move around, able to flow with certain interactions between molecules, not complete free to go anywhere

Chapter 5. (L19)-Chemical Bonds States of matter..Three physical states of matter: Gas, liquid, and solid..The solid state: Like a airplane molecules are closely or densely packed together by strong forces, not free to move around, strong interactions between molecules or ions, crystalline

Chapter 5. (L19)-Chemical Bonds States of matter..Three physical states of matter: Gas, liquid, and solid..Change between states -Between gas phase and liquid phase: vaporization vs. condensation, boiling point -Between liquid phase and solid phase, freezing vs. melting, freezing point, melting point -Between gas phase and solid phase: sublimation (directly from solid to gas) vs. deposition (gas to solid)

Chapter 5. (L19)-Chemical Bonds Theory to explain the states of matter: Intermolecular forces..The change of states from dense phase to loose phase requires energy, while the opposite releases energy..The molecules are held together by intermolecular forces: -Dipole forces -Hydrogen bond -Dispersion forces..Change from dense phase to loose phase needs energy to break the intermolecular forces, while formation of these intermolecular bonding during change from loose phase to dense phase releases energy.

Chapter 5. (L19)-Chemical Bonds Theory to explain the states of matter: Intermolecular forces.. Dipole forces: Occurring between polar molecules of covalent bonding Example: HCl, a dipole, H δ+ —Cl  -, a positive end with H, a negative end with Cl molecular interaction: the positive end attracts the negative end, and so forth, see Fig on pp146..Generally, dipole forces or interactions are much weaker than ionic force, but stronger than the forces between non-polar molecules

Chapter 5. (L19)-Chemical Bonds Theory to explain the states of matter: Intermolecular forces..Hydrogen bond: Occurring between polar molecules containing H and O (or F, N, etc.) Example: H 2 O, asymmetrical polar molecule stronger than ordinary dipole forces hydrogen bond is a special form of dipole forces The dipoles between H and O (or F, N) are much highly polarized, larger  + and  - hydrogen bond occurs between H’s empty valence shell and an unshared electron pair of O or F, or N hydrogen bond is expressed by dotted line (not solid line for covalent bond)

Chapter 5. (L19)-Chemical Bonds Theory to explain the states of matter: Intermolecular forces..Hydrogen bond: Occurring between polar molecules containing H and O (or F, N, etc.) Example: H 2 O asymmetrical polar molecule why water has unusually high melting point and boiling point? It is due to hydrogen bond More examples of hydrogen bond will be discussed in the future

Chapter 5. (L19)-Chemical Bonds Theory to explain the states of matter: Intermolecular forces..Dispersion forces: Occurring to non-polar molecules Example: H 2, O 2, N 2, Cl 2, CH 4 Origin of dispersion force: instant dipole resulting from dynamic movement of electrons between the two atoms. come and go, in very short time a kind of very weak intermolecular force analogy: different ways of holding hands between two people

Chapter 5. (L19)-Chemical Bonds Summary of intermolecular forces Intermolecular forceNature Intensity Dispersion forcenon-polarweakest dipole forcepolarmoderate hydrogen bondpolarstrong

Chapter 5. (L19)-Chemical Bonds Forces in solutions..Solution: An intimate, homogeneous mixtures of two or more substances as if in one phase, Example: salt solution -Intimate: mixing down to the level of individual ions or molecules -Homogeneous: thorough mixing, even with identical physical properties anywhere in the solution

Chapter 5. (L19)-Chemical Bonds Forces in solutions.. Solute: the substance being dissolved, usually present in a smaller amount, e.g., NaCl..Solvent: the substance doing the dissolving, usually present in a larger amount, e.g., H 2 O..Solutions form most readily when the substances with similar bonding characteristics polar solute dissolved in polar solvent non-polar solute dissolved in non-polar solvent

Chapter 5. (L19)-Chemical Bonds Forces in solutions..So called, “like dissolves like” oil in gasoline (to remove grease in car repair work) oil not in water Ethyl alcohol in water organic solvent to remove ink, paint Water solution is also called aqueous solution.

Chapter 5. (L19)-Chemical Bonds How NaCl gets dissolved in water..Process of hydration -the negative end of water molecule will surround a cation to form a very thin “film” of water around the cation, the cation is then hydrated -the positive end of water molecule will surround an anion to form a very thin “film” of water around the anion, the anion is then hydrated Both processes release energy, which can break the ionic bonds between the cations and anions in the solid like NaCl

Chapter 5. (L19)-Chemical Bonds Quiz Time The three kinds of intermolecular forces are (a) dispersion, circulation, and hydrogen bond; (b) ionic attraction, centrifugation, and friction; (c) dispersion, dipole, and hydrogen bond; (d) deposition, sublimation, and evaporation.

Chapter 5. (L19)-Chemical Bonds Quiz Time The dipole forces and hydrogen bond occur between (a) non-polar molecules; (b) ions; (c) ions and non-polar molecules; (d) polar molecules.

Chapter 5. (L19)-Chemical Bonds Quiz Time The dispersion forces between (a) polar molecules; (b) cations and anions; (c) ions and non-polar molecules; (d) non-polar molecules.

Chapter 5. (L19)-Chemical Bonds Quiz Time The order of intensity for the three kinds of intermolecular forces is (a) dispersion > dipole force > hydrogen bond; (b) dipole force > dispersion > hydrogen bond; (c) dipole force > hydrogen bond > dispersion; (d) hydrogen bond > dipole force > dispersion force.

Chapter 5. (L19)-Chemical Bonds Quiz Time The dipole force occurs to which of the following molecules? Is it (a) H 2 ; (b) O 2 ; (c) CH 4 ; (d) HCl.

Chapter 5. (L19)-Chemical Bonds Quiz Time Hydrogen bond does not occur to which of the following molecules? Is it (a) H 2 O; (b) HF; (c) NH 3 ; (d) HI.

Chapter 5. (L19)-Chemical Bonds Quiz Time Water has unusually high melting point and boiling point because of (a) dispersion force; (b) ionic bond; (c) dipole force; (d) hydrogen bond.

Chapter 5. (L19)-Chemical Bonds Quiz Time Sublimation is the change from (a) liquid to solid; (b) liquid to gas; (c) gas to solid; (d) solid to gas.

Chapter 5. (L19)-Chemical Bonds Quiz Time Gaseous molecules of covalent bonding can become liquid and solid because of (a) ionic bonding; (b) friction; (c) gravity; (d) intermolecular forces.

Chapter 5. (L19)-Chemical Bonds Quiz Time Change of states from solid to liquid to gas requires energy because it is needed to break (a) centrifugation; (b) friction; (c) gravity; (d) intermolecular forces or ionic bonding.

Chapter 5. (L19)-Chemical Bonds Quiz Time In a sugar solution, the solute and solvent are respectively (a) water and sugar; (b) sugar and air bubbles; (c) sugar and water; (d) air bubbles and water.