1 / 35

Unit 7 Molecular Geometry

Unit 7 Molecular Geometry. Essential Question. What is a Lewis structure and what does it tell us?. Lewis Structures. Properties are determined by molecular shape Lewis structures can be used to determine shape Shows the arrangement of electrons in a compound. Writing Lewis Structures.

senwe
Télécharger la présentation

Unit 7 Molecular Geometry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Unit 7Molecular Geometry

  2. Essential Question • What is a Lewis structure and what does it tell us?

  3. Lewis Structures • Properties are determined by molecular shape • Lewis structures can be used to determine shape • Shows the arrangement of electrons in a compound

  4. Writing Lewis Structures • Step 1: Add up valence electrons • Ex: H2O H = 1 valence electron X 2 atoms O = 6 valence electrons 8 valence electrons

  5. Writing Lewis Structures • Step 2: Determine the central atom • If Carbon is in the compound, it is the central atom • If Carbon is NOT present, the LEAST electronegative element is central • Hydrogen is NEVER the central atom

  6. Writing Lewis Structures • Step 3: Draw a pair of electrons between the central atom and each bonded atom • A pair of bonding electrons can be represented by a dash or two dots between the bonding atoms H : O : H or H – O – H

  7. Writing Lewis Structures • Step 4: Fill in the rest of the electrons to satisfy the octet rule for all elements in the compound • Hydrogen must satisfy the duet rule .. .. H : O : H or H – O – H .. ..

  8. Writing Lewis Structures • Step 5: Count up all the electrons. Make sure everything has an octet (duet for hydrogen). • If you always check your work, you can’t make a mistake!! • HINT: For these instructions and more helpful tips see page 22 in your packet 

  9. Writing Lewis Structures • If necessary, use two pairs of electrons to form a double bond between two atoms • Ex: CO2

  10. Writing Lewis Structures • If necessary, use three pairs of electrons to form a triple bond between two atoms • Ex: N2

  11. Essential Question • What is polarity?

  12. Polarity • Polar bonds are an intermediate between covalent bonds (equal sharing) and ionic bonds (complete transfer of electrons)

  13. Polarity and Electronegativity • Recall from previous units… • Electronegativity is the ability of an element to attract elements in a compound • High = very attracted to electrons • Low = not so attracted to electrons • Some values can be located on page pg 21 in your packet.

  14. Polarity and Electronegativity • You can determine if a bond is nonpolar covalent, polar, covalent or ionic using electronegativity values (see pg 21 in your packet) • How big is the difference? 3.3 1.7 0.3 0.0 Ionic Polar Covalent Nonpolar Covalent

  15. Now we can determine Lewis structure for a molecule and polarity for a bond • Weren’t we looking for shape??

  16. Essential Questions • What is molecular geometry? • What determines basic molecular geometry?

  17. VSEPR • Valence • Shell • Electron • Pair • Repulsion

  18. VSEPR • VSEPR theory determines the molecular geometry of the molecule • Molecular Geometry – 3D arrangement of a molecule’s atoms in space • Number and type of electron pairs determines shape

  19. VSEPR • We can classify as bonding pairs or lone pairs • Bonding Pair – shared between two atoms • Lone Pair – unshared electrons • Number of each type of electron pair determines shape

  20. VSEPR • Molecular geometry determines the bond angle • Electron pairs avoid each other, so they will stay as far apart as possible • See page 21 in your packet

  21. VSEPR (reference pg 17 or 21 in your packet)

  22. VSEPR • To use determine the shape: • Draw Lewis Structure • Either A - Count the number of lone and bonding pairs, and compare to the chart on the previous slide (this would require you to MEMORIZE the chart) or B - Compare to the chart on page 21 in your packet (that’s what you get on the test)

  23. Molecular Polarity • Some molecules that have polar bonds are nonpolar • Molecular shapes can cause polarity to cancel out

  24. Molecular Polarity • Polar molecules are said to have dipoles • The dipoles tell you which parts of the molecule are slightly negative and slightly positive

  25. Molecular Polarity • For BINARY Compounds • Nonpolar Shapes • Tetrahedral • Linear • Trigonal Planar • Polar Shapes • Pyramidal • Bent

  26. Molecular Polarity • Ternary Compounds will generally be polar • Different elements have different electronegativities, so when there are more than two types of atoms the molecule will not be symetrical

  27. What Does All This Mean?!? • Polarity determines several properties

  28. “Like Dissolves Like” • Polar substances can be dissolved by other polar substances • Nonpolar substances can be dissolved by other nonpolar substances • Polar substances will NOT dissolve in nonpolar substances

  29. “Like Dissolves Like” • When two liquids are capable of mixing, they are miscible • Immiscible means that they will not mix

  30. “Like Dissolves Like” • Water (H2O) is a POLAR substance • So is glass (SiO2) • When water is in a glass container, why does the meniscus curve up?

  31. “Like Dissolves Like” • We know glass is POLAR • Hexane is NONPOLAR • Explain the behavior of this meniscus

  32. “Like Dissolves Like” • Is density the only reason why your salad dressing separates??

  33. More Properties

  34. More Properties

  35. What type of bear dissolves in water??

More Related