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Understanding Resonance Structures and Electron Delocalization in Chemistry

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Resonance structures depict how electrons are shared among multiple bonds in molecules, highlighting the concept of delocalization. This phenomenon can be identified by examining bond lengths and angles. For example, in the formate ion (HCOO-), the C-O bond lengths are shorter than those of a single bond yet longer than a double bond, indicating resonance. Additionally, resonance hybrids represent the extremes of these structures, with the actual structure being a blend. Curved arrows illustrate electron movement, while dashed lines can symbolize partial bonds.

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Understanding Resonance Structures and Electron Delocalization in Chemistry

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  1. HL Bonding Resonance Structures & Delocalisation of Electrons

  2. Resonance Structures • Occurs when electrons are “shared” between more than one bond

  3. Resonance Structures • Occurs when electrons are “shared” between more than one bond • Presence can be identified from bond lengths and bond angles

  4. Resonance Structures • Occurs when electrons are “shared” between more than one bond • Presence can be identified from bond lengths and bond angles • E.g. HCOO- has C to O bond lengths of 0.127 nm, which are shorter than a single bond and longer than a double bond

  5. Resonance Structures of HCOO- From: www.mpcfaculty.net/mark_bishop/resonance.htm

  6. Resonance Structures • These different structures are known as resonance hybrids

  7. Resonance Structures • These different structures are known as resonance hybrids • These are the extreme forms with the actual structure somewhere in between

  8. Resonance Structures • These different structures are known as resonance hybrids • These are the extreme forms with the actual structure somewhere in between • A double-headed arrow is always used to show resonance structures

  9. Resonance Structures • These different structures are known as resonance hybrids • These are the extreme forms with the actual structure somewhere in between • A double-headed arrow is always used to show resonance structures • This process of electrons “spreading out” is called delocalisation

  10. e.g. ozone From: http://academic.reed.edu/chemistry/roco/Resonance/major_minor.html

  11. e.g. ozone Instead of drawing the resonance structures, a dotted/dashed line may be used to represent a partial bond. From: http://academic.reed.edu/chemistry/roco/Resonance/major_minor.html

  12. e.g. CO32- From: http://www.mhhe.com/physsci/chemistry/carey/student/olc/graphics/carey04oc/ch01/figures/res1.gif

  13. e.g. benzene From: http://mooni.fccj.org/~ethall/benzene/benzene.htm

  14. e.g. benzene As the C-C-H bond angles in benzene are 120 °, the carbon atoms are sp2 hybridized, with the remaining p electron being delocalised From: http://mooni.fccj.org/~ethall/benzene/benzene.htm

  15. Can you draw 3 resonance structures for NO3-?

  16. Can you draw 3 resonance structures for NO3-? From: http://en.wikipedia.org/wiki/Image:Nitrate_ion_resonance_structures.png

  17. Can you draw 3 resonance structures for SO32-?

  18. Can you draw 3 resonance structures for SO32-?

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