A simple procedure for writing Lewis structures is given in a previous
article entitled “Lewis
Structures and the Octet Rule”. Relevant worked examples were given in the following
articles: Examples #1,
#2,
#3
, #4,
#5,
#6,
#7,
#8, #9, #10, #11, #12,
#13, #14, #15, #16, #17, #18, #19, #20, #21, #22, #23, #24, #25, #26, #27 and #28.
Let us consider the case of the pentazenium or pentanitrogen N5+ cation. This highly explosive cation was first synthesized and isolated as a salt by K.O. Christie in 1999 by the reaction of N2F+ with HN3 . The N5+ cation was the first new all nitrogen species to be synthesized in isolable quantities in more than a century, and only the third ever produced. Prior to this nitrogen cation only molecular N2 , isolated in 1772 and the azide ion N3- , first synthesized in 1890, had ever been isolated. The overall objective of Christie's research was the synthesis and characterization of polynitrogen, high-nitrogen and high-oxy gen energetic materials, useful as propellants or explosive ingredients.
Step 1: Connect the atoms with
single bonds.
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Fig. 1: Connecting the atoms of the N5+ cation with single bonds |
Step 2: Calculate the # of electrons in π bonds (multiple bonds) using formula (1):
Where n in this
case is 5 since N5+ consists of 5 atoms.
Where V = (5 * 5
) - charge = 25 – 1 = 24, V is the number of the valence electrons in the ion.
Therefore, P = 6n
+ 2 – V = 6 *5 + 2 – 24 = 8 \ there are: 1) either 4 double bonds 2) or
2 triple bonds 3) or 1 triple and 2
double bonds.
Step 3 & 4: The Lewis structure of N5+ is as follows:
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Figure 2: Lewis electron dot structures for the N5+
ion. The least plausible structures are
#1 (+ charges adjacent to each other) and #3 (large charge separation).
|
Therefore, five resonance electron dot structures were derived for the N5+ion.