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Short Tips on Wade's Rule

Dear students wade's rule is a most important topic to be prepare before exam
many of students get confuse with distinct formulas but actually by this trick I will give  you a short hand ...

The general methodology to be followed when applying Wade's rules is as follows:
1. Determine the total number of valence electrons from the chemical formula, i.e., 3 electrons per B, and 1 electron per H.

2. Subtract 2 electrons for each B-H unit (or C-H in a carborane).

3. Divide the number of remaining electrons by 2 to get the number of skeletal electron pairs (SEP).

4. A cluster with n vertices (i.e., n boron atoms) and n+1 SEP for bonding has a closo structure.

5. A cluster with n-1 vertices (i.e., n-1 boron atoms) and n+1 SEP for bonding has a nido structure.

6. A cluster with n-2 vertices (i.e., n-2 boron atoms) and n+1 SEP for bonding has an arachno structure.

7. A cluster with n-3 vertices (i.e., n-3 boron atoms) and n+1 SEP for bonding has an hypho structure.

8. If the number of boron atoms (i.e., n) is larger than n+1 SEP then the extra boron occupies a capping position on a triangular phase.


Example 1

What is the structure of B5H11?

1. Total number of valence electrons = (5 x B) + (11 x H) = (5 x 3) + (11 x 1) = 26
2. Number of electrons for each B-H unit = (5 x 2) = 10
3. Number of skeletal electrons = 26 10 = 16
4. Number SEP = 16/2 = 8
5. If n+1 = 8 and n-2 = 5 boron atoms, then n = 7
6. Structure of n = 7 is pentagonal bipyramid (Figure 2), therefore B5H11 is an arachno based
upon a pentagonal bipyramid with two apexes missing
author

DESH DEEPAK A P S CHAUHAN

M.Sc. CHEMISTRY!

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