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VSPER

VSPER. Molecular shapes Valence Shell Electron Repulsion Theory. VSEPR Theory. • Covalent bonds consist of shared pairs of electrons • These electrons must exist between the atoms sharing them • Electron pairs are negatively charged and must repel each other

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VSPER

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  1. VSPER Molecular shapes Valence Shell Electron Repulsion Theory

  2. VSEPR Theory • Covalent bonds consist of shared pairs of electrons • These electrons must exist between the atoms sharing them • Electron pairs are negatively charged and must repel each other • These repulsions force the molecule to exist in a specific arrangement of atoms or shape

  3. So… • In Valence Shell Electron Pair Repulsion (VSEPR) theory, pairs of electrons that surround the central atom of a molecule or ion are arranged as far apart as possible to minimise electron-electron repulsion.

  4. What does this mean? • Essentially… • Electrons have a mutually repulsive force- they repel each other due to their negative charge • The shape of the charge cloud affects how much it repels other charge clouds • Where electrons are involved in bonding they have a different repulsive effect than lone pairs- those not used in bonding • Produces predictable shapes

  5. So… • Greatest angles between lone pairs- bonding pairs produce somewhat lower angles • Presence or absence of lone pairs will affect overall shape of the molecule

  6. This Idea Is Easily Seen With Balloons Tied Together • The Shapes of 2, 3, and 4 • Repulsions

  7. In summary- • Lone pair/lone pair bonds largest angle • Lone pair/bonding pair next lowest • Bonding pair/bonding pair lowest • Simples…..? • Lets start with bonded pairs

  8. Linear • Atoms in a straight line- examples • Two bonding pairs- only- angle 180o • Beryllium Chloride (BeCl2) • Carbon Dioxide (CO2) • What's the difference?

  9. Single bonds and double/triple bonds do not affect the overall shape of the molecule! • Just as well as this is complex enough as it stands!

  10. Trigonal planar • Triangular/flat- three bonding pairs- angles 120o • Example- Boron Trichloride (BCl3)

  11. Ethene (C2H4)is similar, but consists of two sets of three bonds- still trigonal planar

  12. Tetrahedral • Four bonding pairs- angles 109.5o • Example methane (CH4)

  13. Trigonal Bipyramidal • Five bonding pairs- 90o and 120o • Example- phosphorous fluoride (PF3)

  14. Octahedral • Six bonding pairs- all 90o • Example- Sulphur Hexafluoride (SF6)

  15. What about lone pairs? • Alters the angle- effectively 'bends' the molecule- non linear • Example- planar- water (H2O) • Bonding angle 104.5o- due to two lone pairs

  16. Pyramidal • Again, three bonding pairs • Example- ammonia (NH3) • One lone pair- bonding angle 107o

  17. CommonBondingGeometries AB2 AB2 AB3 AB4 • Atoms (B) which are bonded to a central atom (A): ABn

  18. tetrahedron 109.5o trigonal planar 120o linear 180o Each shape is associated with particular angles

  19. Each shape is associated with specific angles

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