How do you draw double and triple bonds in Lewis Symbols?

1 Answer
anor277
Dec 17, 2016

Let's look at 2 small molecules: #"acetylene"#; and #"hydrogen cyanide"#.

Explanation:

Both molecules contain formal triple bonds.

#"Acetylene:"# #C_2H_2#; there are #2xx4(C)+2(H)# #"valence electrons"#, thus #10# valence electrons to distribute.

#H-C-=C-H#

#"Hydrogen cyanide:"# #HCN#; there are #4(C)+5(N)+1(H)# #"valence electrons"#, thus #10# valence electrons to distribute.

#H-C-=N:#

At the nitrogen centre 2 of the valence electrons are lone-pair, and thus the nitrogen is associated with #2("inner shell")+2("lone pair)"+3("C-N triple bond)= 7 electrons"#, whose charge is balanced by the 7 protons in the nitrogen nucleus. Are you happy with this?

Can you similarly account for the bonding in #"ethylene"#, #H_2C=CH_2#, with #"12 valence electrons"#?

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