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Intermolecular Forces (IMF) Tutorial & Questions

By Francis Nichols,2014-06-19 06:46
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Intermolecular Forces (IMF) Tutorial & Questions

    Name: _____________________________________________ Hr: _________ Date: ______ Intermolecular Forces (IMF) Tutorial & Questions

    This tutorial (and many others) at:

    http://www2.wwnorton.com/college/chemistry/gilbert/tutorials/ch9.htm

    Below is the text from the tutorial. It is strongly recommended you include detailed and labeled diagrams. The questions are requiredthey are italicized (last 2 pages)

    1. The strength of the intermolecular forces (IMF) in a substance determines many of its macroscopic

    properties, including melting point, boiling point, phase at room temperature, solubility, and miscibility

    (ability to mix uniformly).

    2. Just as an interstate highway runs between states, intermolecular forces are attractions between

    molecules. In contrast, intramolecular forces occur within a molecule and include covalent bonds

    between atoms.

    3. A single ionic molecule, like NaCl, is held together by the attraction between opposite charges

    (electrostatic attraction). The attraction is called an ionic bond.

    A large sample of NaCl is also held together by attractions between opposite charges. These

    attractions, called ion-ion forces, are the strongest kind of IMF.

    When several formula units of an ionic compound “join” they form a crystal lattice. The amount of

    energy required to break the lattice (i.e. separate the formula units) is called lattice energy. The

    strength of the ion-ion forces (or lattice energy) for a substance can be estimated using 2 factors:

    a) product of the charges of the atoms (absolute value): higher the product, stronger the

    attraction

    b) distance between nuclei (atomic radius): larger the distance, weaker the attraction

    4. As you have seen, electronegativity difference between covalently bonded atoms in a molecule can

    result in a bond dipole.

    Two polar molecules are attracted by dipole-dipole forces.

    As the polarity of the covalent bond increases, so will the dipole-dipole forces.

    Name: _____________________________________________ Hr: _________ Date: ______ 5. Hydrogen bonding is a special kind of dipole-dipole attraction that occurs with a hydrogen atom

    covalently bonded to N, O, or F.

    H-bonding between molecules is the strongest kind of dipole-dipole attraction.

    6. Dispersion forces, or London forces, occur when the electron clouds of two molecules within close

    proximity of each other are distorted because of the repulsion between the electrons. The atomic

    charge distribution is disrupted for a split second, resulting in a brief dipole moment, or induced dipole,

    with one side of the molecule becoming slightly more negative, and the other side slightly more positive.

    This dipole can then induce dipoles in other nearby molecules. These dipoles fluctuate rapidly.

    7. It is important to remember the relative strengths of the different IMF because it relates to melting point

    and boiling point (and, therefore, phase at room temperature).

    Stonger IMF =

    Weaker IMF =

    8. Two liquids are miscible if they exhibit similar IMF. For example, oil and water do not mix because

    nonpolar liquids are immiscible with polar liquids.

    A substance is soluble if the IMF between solute and solvent overcome the IMF between solute

    molecule.

    Ion-dipole forces occur between an ionic solute and a polar solvent

    Dipole-induced dipole force can occur between a nonpolar solute and a polar solvent (although this

    does not usually occur)

9. Question 1: Rank the following from strongest to weakest IMF: He, NH, NF, and NaCl 33

    Name: _____________________________________________ Hr: _________ Date: ______

    10. Question 2: Rank the following from strongest to weakest IMF: HF, F, and FCl 2

    11. Question 3: Rank the following from strongest to weakest (use charge multiple and nuclei distance):

    NaCl, MgCl, AlCl, MgS, and NaBr 23

    12. Are NH and HO miscible? 32

    13. Would you expect KBr to be a solid, liquid, or gas at room temp? Explain.

This tutorial (and many others) at:

    http://www2.wwnorton.com/college/chemistry/gilbert/tutorials/ch9.htm

Questions from the text: Ch 14, section 1. Read the entire section, focus on IMF.

    14. According to the kinetic-molecular theory, the state of a substance at room temp depends on what?

    Describe the difference between solids, liquids, gases based on this concept.

    15. List the 3 types of intramolecular forces (i.e. the 3 types of bonds):

    16. All ionic compounds, and most metallic compounds, are solids at room temperature. What can one

    conclude about the strength of the IMF of these substances?

    17. Complete the statement: “Whether a substance is a molecular solid, liquid, or gas at room temperature

    does _________ depend on the strength of _____________________ forces. Rather, it depends on

    how strongly the _____________________ of that substance attract to one another (i.e. intermolecular

    forces).

    18. How does an intramolecular force differ from an intermolecular force?

    19. Which are generally stronger: intramolecular forces or intermolecular forces?

    Name: _____________________________________________ Hr: _________ Date: ______ 20. Describe what is occurring in each section (a, b, and c) of Figure 14-8 on p. 463. Read past this

    diagram in order to learn essential information.

    21. Dispersion forces increase as the atomic radius (size) of the involved atoms increases. Why?

    22. How do dipole-dipole forces differ from dispersion (or “induced dipole”) forces? Draw a diagram of how

    two OBr molecules would orient themselves around each other. Use the structural formulas of the 2

    OBr molecules, include partial charge symbols, and use a dashed line to symbolize the dipole-dipole 2

    link between the molecules.

    23. Hydrogen bonding is a type of dipole-dipole force involving the H of one molecule and what 3 other

    atoms of another molecule? (BTW: H bonding occurs because these 3 atoms are extremely

    electronegative and H is not so electronegative). Draw a diagram of how two water molecules would

    orient themselves around each other. Use the structural formulas of the water molecules, include

    partial charge symbols, and use a dashed line to symbolize the dipole-dipole link between the

    molecules.

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