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Chemistry LibreTexts

Exercises

  • Page ID
    54338
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    Section 4-1

    Q1-1

    Make a model of CH4

    A) Draw a picture of it – try to include all the aspects of the model –show its 3D structure, and bond angles. Compare your picture with others around you – do they look the same?

    Q1-2

    Now make a model of C2H6, draw a picture of it. Compare your picture with others around you – do they look the same? Are they easily recognizable as the same thing?

    Q1-3

    What if you wanted to draw a “quick” picture of the structure. What would that look like? (draw it)

    Q1-4

    Now draw a Lewis structure for CH4 and C2H6

    • Compare to your neighbors – do they look the same? Why or why not?

    Q1-5

    What information is missing from a Lewis structure?

    Section 4-2

    Q2-1

    Draw the Lewis structure for H2O

    Q2-2

    Draw the Lewis structures for NH4+

    Q2-3

    Draw the Lewis structure for C2H6O

    Q2-4

    Draw the Lewis structure for HCN

    Q2-5

    Draw the Lewis structure for CH4O

    Q2-6

    Draw the Lewis structure for CH3CHO

    Q2-7

    Fill in the following chart.

    Section 4-3

    Formula

    Lewis Structure

    Electron Pair geometry,

    Bond Angle(s)

    Molecular Shape

    Bond Angles

    Hybridization of atoms bonded to more than one other atom

    H2O

    Tetrahedral,

    ~109

    Bent

    ~109

    O = sp3

    C3H6

    H3O+

    O3

    NO3

    CH3CHO

    CH3OCH3

    SCN

    Section 4-4

    Q4-1

    How many different compounds can you draw for the formula C5H12?

    Q4-2

    Is there a generic formula for an alkane containing “n” carbon atoms?

    Q4-3

    How would this generic formula change if you joined the ends of a carbon chain and made a ring? (for example cyclohexane has six carbons in a ring - how many hydrogens would it have?)

    Q4-4

    How would this generic formula change if you had a double bond in there instead of all single bonds? – how about a triple bond?

    Q4-5

    Hydrocarbons are non-polar, we can assume they only have London Dispersion Forces between molecules. Make a prediction as to the melting and boiling points of ethane, compared to methane; what assumptions are you making?

    Q4-6

    In general how will boiling points and melting points of hydrocarbons change as the molecular weight increases? Why?

    Section 4-5

    Download the PhET applet from

    http://phet.colorado.edu/en/simulation/molecule-shapes

    and use it to help you complete this worksheet. You will need to have the Lewis structures which were already sent to you as answers in a previous email. (Or you can redraw them.)

    Formula

    Electron pair geometry

    Molecular shape

    Hybridization

    NH3

    NH4+

    NH2-

    C2H2

    SO3

    HNO3

    CH3CH2OH

    What things about the molecular shape are the same as the electron pair geometry? What things are different?

    Section 4-6

    For each formula draw the Lewis structure, the condensed structure and the line structure (there are 4 possible for C6H12 and two for C2H7N)

    Formula

    Lewis structure

    Condensed Structure

    Line structure

    C6H12

    C6H12

    C6H12

    C6H12

    C2H7N

    C2H7N

    Section 4-8

    Go to http://phet.colorado.edu/en/simulation/molecule-polarity

    AND http://phet.colorado.edu/en/simulation/molecule-shapes

    • Download both simulations and play around with them some – in one alter what is connected to an atom (i.e. single, double, triple bonds, or lone pairs) to determine geometry and shape and in the other change the electronegativity and watch the bond polarities and molecular polarity change.
    • For each molecule below, first draw the Lewis structure. Then using the Lewis structure predict the structure’s geometry and shape, if it has a partial positive or negative charge make sure you label it, draw the bond dipoles and then predict the direction of the molecular dipole and if the molecule is polar.
    • Check your answer using the applets.

    Lewis structure

    e- pair geometry

    (e-geometry)

    Molecular shape (molecule geometry)

    Draw the direction of all polar bonds and if there is a molecular dipole

    Is the molecule polar?

    H2O

    NO3-

    CH2O

    CH3F

    CF4

    BF3

    CH2Cl2

    Section 4-9

    Q9-1

    Draw out 4 molecules of HF showing how they interact with each other

    Q9-2

    Draw out 4 molecules of H2O showing how they interact with each other

    Q9-3

    Draw out 4 molecules of CH3OH showing how they interact with each other

    Q9-4

    Draw out 4 molecules of CH3OCH3 showing how they interact with each other

    Section 4-10

    Q10-1

    Why are the interactions between H2O molecules stronger than those between HF molecules, even though the polarity of the HF bond is larger than the polarity of the OH bond.

    Q10-2

    Why don’t more than four water molecules interact with a central water molecule?

    Q10-3

    What would you predict would be the relative boiling points of methanol (CH3OH) and ethane (CH3CH3) - which have similar molecular weights? Explain your answer.

    Q10-4

    What would you predict would be the relative boiling points of methanol (CH3OH) and ethanol (CH3CH2OH)? Explain your answer.

    Section 4-12

    Q12-1

    What is an ion?

    Q12-2

    What is an ionic compound? Can you provide an example?

    Q12-3

    What is the difference between an ionic and a covalent bond?

    Q12-4

    What kinds of compounds are likely to be ionic? (How would you spot them?)

    Section 4-13

    Q13-1

    Draw a picture of what you imagine solid sodium chloride looks like at the atomic level.

    Q13-2

    Draw a molecular level picture of liquid water, and a molecular level picture of liquid sodium chloride. Use this picture to help explain why it takes more energy melt solid salt than it does to melt solid water. (What interactions have to be overcome to melt each substance?)

    Q13-3

    Why doesn’t solid sodium chloride conduct electricity, but solid aluminum does?

    Q13-4

    Why does molten (liquid) sodium chloride conduct electricity? Is it the same reason as for Aluminum?

    Q13-5

    Arrange these ionic compounds in order of increasing melting point. NaCl, KBr, CaO, Al2O3. Look up your answers and see if your predictions were correct. What factors did you take into account when making these predictions?

    Q13-6

    Arrange these materials in order of increasing melting point. CH4, MgBr2, HF, C(diamond) Look up your answers and see if your predictions were correct. What factors did you take into account when making these predictions?

    More Lewis Structures

    Formula

    Lewis Structure

    Formula

    Lewis Structure

    C4H10

    H3O+

    C5H12

    NH4+

    C2H4

    NH2-

    C2H2

    CH3CHO

    H2O

    SO3

    NH3

    NO3-

    CH3CH2OH

    SCN-

    C2H7N

    O3


    Exercises is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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