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VSPER Web Exercises

Here are some questions to challenge yourself based on the previous notes given .

This link will lead you to the question with the solutions and some tips to tackle the questions.

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Example Questions :

1.       Based on VSEPR model, which of the following molecule(s) is (are) planar

 i.       NH₃         

 ii.       BF₃               

iii.       CH₄

A.       i only     

B.       ii only     

C.       iii only                                                                                      Answer : B

D.       i &  ii                                                                                       

E.       ii & iii

F.       None of the above. 

Explanation :
 - NH_{3 -}  there is a lone pair in the outer shell of the central N atom of NH3. 
In NH3 the N has 3 bond pairs and 1 lone pair, (4 total pairs). The shape is called trigonal pyramidal (approximately tetrahedral minus one atom).

-  BF_{3 -} shape is trigonal planar. You know that B is the central atom, and the F's are on the outside. After you draw it out, you'll notice it has 0 lone pairs, and 3 bonding pairs, thus making it a trigonal planar.

- CH<sub>4 - tetrahedral.






2. What is the arrangement of electron pairs and molecular structure of using</sub> SF₄ VSPER theory ?


Answer : The arrangement is trigonal bipyramidal and the molecular structure is see-saw shape.






3. Draw the geometric structure of PCl₅ using VSPER theory.


Answer :

5 + (5 x 7) = 40 electrons
(5 single bonds = 10 electrons; 3 lone pairs on each Cl atom = 30 electrons, hence AX₅ (trigonal pyramidal))

Bonding : VSPER Theory

VSPER THEORY

• Valence Shell Electron Pair Repulsion theory (VSEPR) is a set of rules whereby the chemist may predict the shape of an isolated molecule. 

• It is based on the premise that groups of electrons surrounding a central atom repel each other, and that to minimize the overall energy of the molecule, these groups of electrons try to get as far apart as possible. 

• Groups of electrons can refer to electrons that participate in a bond (single, double, or triple) to another atom, or to non-bonding electrons (e.g. lone pair electrons).

• Since the molecular geometry is determined by how many bonding and non-bonding electron groups surround the central atom, the first thing one needs to do is count how many of each there are. 

Summary VSPER table

_{keyword :
A : Central Atom.
X : Electron Domain.
E : Lone Pairs}

MUST SEE VIDEO :

This video might help you to understand VSPER theory better.

 Other VIDEO :




Some basic information on VSEPR theory and the geometry formed by electron pairs around a central atom. Discussed in this video are linear, trigonal planar, and tetrahedral arrangements.

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