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Shapes of molecules & ions

Shapes of molecules & ions. VSEPR theory. VSEPR - the V alence S hell E lectron P air R epulsion theory is used to obtain the shape of simple molecules and ions. VSEPR theory.

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Shapes of molecules & ions

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  1. Shapes of molecules & ions

  2. VSEPR theory • VSEPR - the Valence Shell Electron Pair Repulsion theory is used to obtain the shape of simple molecules and ions

  3. VSEPR theory • VSEPR - the Valence Shell Electron Pair Repulsion theory is used to obtain the shape of simple molecules and ions • It states that because of the repulsion between pairs of electrons around the central atom in the molecule or ion, the pairs of electrons are arranged to be as far away from each other as possible

  4. Negative Charge Centres • For VSEPR, multiple bonds (double, triple) count as if they are just one pair of electrons

  5. Negative Charge Centres • For VSEPR, multiple bonds (double, triple) count as if they are just one pair of electrons • So VSEPR uses repulsion between negative charge centres rather than between pairs of electrons

  6. 4 negative charge centres • 4 bonding pairs - tetrahedral • Bond Angle = 109.5º • E.g methane - CH4, CCl4, SiCl4 From: http://library.thinkquest.org/3659/structures/commonstructures.html www.chemvc.com/~tim/VSEPR.html , http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter4section8.rhtml

  7. 4 negative charge centres • 3 bonding pairs (& 1 non-bonding pair) • trigonal pyramid • Bond Angle = 107º • E.g. ammonia - NH3, PCl3 From: http://library.thinkquest.org/3659/structures/commonstructures.html www.chemvc.com/~tim/VSEPR.html , http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter4section8.rhtml

  8. The bond angle decreases because the non-bonding pair of electrons exerts a greater repulsion than the bonding pair(s) From: http://www.examstutor.com/chemistry/resources/studyroom/bonding/shapes_of_molecules/

  9. 4 negative charge centres • 2 bonding pairs ( 2 non-bonding pairs) • bent or v-shaped • Bond angle = 105º • E.g. H2O, H2S From: http://library.thinkquest.org/3659/structures/commonstructures.html www.chemvc.com/~tim/VSEPR.html , http://www.sparknotes.com/testprep/books/sat2/chemistry/chapter4section8.rhtml

  10. 2 negative charge centres • Shape is always linear • Bond angle is 180º • E.g. From: www.physchem.co.za/Bonding/Shape.htm www.tulane.edu/~bmitche/book/structrj.html

  11. 3 bonding electron pairs, no non-bonding pairs Trigonal planar Bond angle is 120° e.g. BF3, ethene, CO32- 2 bonding pairs, 1 non-bonding pair Bent or v-shaped Bond angle is 120° E.g. SO2, ozone - O3 3 negative charge centres From: http://library.thinkquest.org/3659/structures/commonstructures.html , www.chm.bris.ac.uk/motm/so2/so2h.htm

  12. 5 and 6 charge centres • Elements in the third period can have more than 8 electrons in their outer shell because the 3 d orbitals are close in energy to the 3p orbitals. • The VSEPR theory also applies • You do not have to know specific bond angles

  13. 5 negative charge centres (HL) • Trigonal bipyramidal e.g. PCl5 From: http://library.thinkquest.org/3659/structures/commonstructures.html

  14. 5 negative charge centres (HL) • 4 bonding pairs and 1 non-bonding pair • Distorted tetrahedral From: www.chemvc.com/~tim/Predictions.html

  15. 6 negative charge centres (HL) • Octahedral • e.g. SF6 From: http://library.thinkquest.org/3659/structures/commonstructures.html

  16. 6 negative charge centres (HL) • 4 bonding pairs and 2 non-bonding pairs as far apart as possible (above & below plane) • Square planar • e.g. XeF4 From: www.chemvc.com/~tim/Predictions.html

  17. VESPR theory • All the previous molecular shapes are based on VSEPR theory • VSEPR=Valence Shell Electron Pair Repulsion theory • Pairs of electrons arrange themselves around the central atom so that they are as far apart from each other as possible

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