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Molecular Structures. CH 4. Gumdrop Molecule Activity . Draw the L ewis dot structure for the molecule Use gumdrops, marshmallows, and toothpicks to build a 3D representation of the molecule Gumdrop=atom Toothpick=bond Small marshmallow=shared electron pair

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Molecular Structures

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Molecular Structures


CH4


Gumdrop Molecule Activity

  • Draw the Lewis dot structure for the molecule

  • Use gumdrops, marshmallows, and toothpicks to build a 3D representation of the molecule

    • Gumdrop=atom

    • Toothpick=bond

    • Small marshmallow=shared electron pair

    • Large marshmallow=lone electron pair

  • Draw a sketch on sheet of your molecule (remember a key!)


Lets look at Methane (CH4)…

  • What do you notice about methane?

    • How many shared electron pairs are surrounding the central carbon?

      • Enter number into Quizdom Remote


Lets look at Methane (CH4)…

  • What do you notice about methane?

    • Can it bond with anything else?

      • Yes

      • No


Lets look at Methane (CH4)…

  • 3D Model: Jmol perspective

    • Bond Angle: 109.5°

  • Molecular Shape Name:

    • Tetrahedral

    • 4 pairs. All Shared.


NH3


Gumdrop Molecule Activity

  • Draw the Lewis dot structure for the molecule

  • Use gumdrops, marshmallows, and toothpicks to build a 3D representation of the molecule

    • Gumdrop=atom

    • Toothpick=bond

    • Small marshmallow=shared electron pair

    • Large marshmallow=lone electron pair

  • Draw a sketch on sheet of your molecule (remember a key!)


Now, how about Ammonia (NH3)?

  • How many shared pairs of electrons are there?


Now, how about Ammonia (NH3)?

  • How many shared pairs of electrons are there?

  • Predict what you think will happen to the bond angles between the hydrogens in ammonia compared to the hydrogens in methane:

    • A) The angle will increase

    • B) The angle will decrease

    • C) The angle will remain the same


Lets look at Ammonia (NH3)…

  • 3D Model: Jmol perspective

    • With lone pairs

    • Bond Angle: 107.6°

  • Molecular Shape Name:

    • Trigonalpyramidal

    • 4 pairs: 3 shared. 1 lone pair


What would happen if there was no Lone pair on Ammonia?


BH3


For bH3…

  • How many unshared pairs of electrons exist around the central atom?


What does BH3 look like?

  • 3D Model: Jmol perspective

    • Bond Angle: 120°

  • Molecular Shape Name:

    • Trigonalplanar

    • 3 pairs: 3 shared. 0 lone pair


H2O


Now Let’s take another Electron pair off…What will H2O look like?

  • Which is NOT true about the relationship between water and ammonia?

    • A) The bond angle is greater for water than it is for ammonia

    • B) The bond angle is smaller for water than it is for ammonia

    • C) There are more lone pairs in water

    • D) There are fewer shared pairs in water


H2O…it’s everywhere

  • 3D Model: Jmol perspective

    • With Lone Pairs

    • Bond Angle: 104.5°

  • Molecular Shape Name:

    • Bent

    • 4 pairs: 2 shared. 2 lone pair


CO2


What is different for CO2?

  • How many lone pairs are there?


What is different for CO2?

  • How many lone pairs are there?

  • How many covalent bonds are formed around the carbon?


Let’s look at CO2…

  • 3D Model: Jmol perspective

    • Bond Angle: 180°

  • Molecular Shape Name:

    • Linear

    • 4 pairs: 4 shared. 0lone pair


Easy Enough…Lets see if we can use our chart to predict for other Molecules


What do you think about BeCl2?

  • How many shared pairs are there?


What do you think about BeCl2?

  • How many shared pairs are there?

  • How many lone pairs are there around the central atom?


Now Let’s look at H2S

  • How many lone pairs are there?


Now Let’s look at H2S

  • How many lone pairs are there?

  • What would the bond angle be?


For PH3…

  • How many lone pairs are there?


For PH3…

  • How many lone pairs are there?

  • The bond angle for PH3is ______ compared to CH4.

    • A) Larger

    • B) Smaller

    • C) The same


How about CCl4?

  • How many shared pairs around central atom?


How about CCl4?

  • How many shared pairs around central atom?

  • How many lone pairs?


How about CCl4?

  • How many shared pairs around central atom?

  • How many lone pairs?

  • What would you predict the bond angle would be?


PCl5


Expanded Octet: PCl5

  • TrigonalBipyramidal

    • Jmol representation

    • Bond Angles: 90° and 120°

    • 5 Total Pairs: 5 Shared pairs 0 Lone Pairs


Expaned Octet… Cont.

  • Octahedral : SF6

    • Jmol Representation

    • Bond Angles: 90°

    • 6 Total Pairs: 6 shared, 0 Lone Pairs


Octahedral : SF6

What do you think would happen if you removed an Fluorine from the central Sulfur atom?

What if you removed another?

How do you think this would affect the molecular model?


Valence Shell Electron Pair Repulsion Theory

The molecular structure is based on electrons (Shared or unshared) arranging themselves so that they have the greatest distance between one another around the central atom.

The goal is to minimize the repulsion between the negatively-charged electrons.


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