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Valence-Shell Electron-Pair Repulsion Theory

Valence-Shell Electron-Pair Repulsion Theory. Gillespie and Nyholm developed model in 1957 Predicts shape of molecules Fundamental principle: the bonding pairs and lone pairs of electrons in the valance level of an atom repel one another due to their negative charges. VSEPR Theory.

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Valence-Shell Electron-Pair Repulsion Theory

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  1. Valence-Shell Electron-Pair Repulsion Theory

  2. Gillespie and Nyholm developed model in 1957 Predicts shape of molecules Fundamental principle: the bonding pairs and lone pairs of electrons in the valance level of an atom repel one another due to their negative charges. VSEPR Theory

  3. VSEPR Continued… • Pairs of electrons around the central atom try to be as far away from one another as possible while remaining in the molecule • Lone pair electrons will spread out more than bonding pair electrons • This means the repulsion is greatest between lone pairs • Bonding pairs are more localized between nuclei so they spread out less than lone pairs • The repulsion between lone pairs and bonding pairs is in between repulsions for lone to lone pairs, and bonding to bonding pairs • Can be expressed in decreasing order of repulsion: LP-LP>LP-BP>BP-BP

  4. VSEPER Continued • Double bonds(two bonding pairs), triple bonds(three bonding pairs) act as single electron group when repelling other groups of electrons • You can determine the shape of the molecule around the atom by analyzing the types and number of electron pairs around the central atom • We will be looking at five different shapes that atoms can form but there are many more that we will not discuss.

  5. Linear Shape • Two electron groupings around central atom • Can be a combination of two double bonds or a single and triple bond • Bond angle, which is the angle formed by two bonds is 180° in a linear shape • Two dimensional • Examples: CO2

  6. Trigonal Planar • Three electron groupings around central atom • Can be a combination of two single bonds and one double bond or three single bonds • Bond angle is 120 ° • Two dimensional • Examples: CH2O

  7. Tetrahedral • Four electron groupings around central atom • All bonding pairs has four single bonds • Completely symmetrical • Bond angles are each 109.5 ° • Three dimensional • Example: CH4

  8. Pyramidal • Four electron groupings around the central atom • One lone pair of electrons and three single bonds • Bond angle less than 109 °(because the lone pair exerts a stronger force on the bonding pairs than they do on eachother • Example: NH3

  9. Bent • Four electron groupings around central atom • Two lone pairs, two single bonds • Bond angle is 104.5 °(two lone pairs reduce two bonding pairs even more than pyramidal shape) • Example: H2O

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