shapes of molecules & ions. vsepr theory vsepr - the valence shell electron pair repulsion...
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VSEPR theory
VSEPR - the Valence Shell Electron Pair Repulsion theory is used to obtain the shape of simple molecules and ions
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
Negative Charge Centres
For VSEPR, multiple bonds (double, triple) count as if they are just one pair of electrons
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
4 bonding pairs - tetrahedral
Bond Angle =
109.5º
E.g methane - CH4, CCl4, SiCl4
4 negative charge centres
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
3 bonding pairs (& 1 non-bonding pair) trigonal pyramid
Bond Angle = 107º
E.g. ammonia - NH3, PCl3
4 negative charge centres
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
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/
2 bonding pairs ( 2 non-bonding pairs)
bent or v-shaped
Bond angle = 105º
E.g. H2O, H2S
4 negative charge centres
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
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
3 negative charge centres 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
From: http://library.thinkquest.org/3659/structures/commonstructures.html ,
www.chm.bris.ac.uk/motm/so2/so2h.htm
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
5 negative charge centres (HL)
Trigonal bipyramidal e.g. PCl5
From: http://library.thinkquest.org/3659/structures/commonstructures.html
5 negative charge centres (HL)
4 bonding pairs and 1 non-bonding pair
Distorted tetrahedral
From: www.chemvc.com/~tim/Predictions.html
6 negative charge centres (HL)
Octahedral
e.g. SF6
From: http://library.thinkquest.org/3659/structures/commonstructures.html
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
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