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Lewis Base Shorthand

Posted: Mon Oct 30, 2017 1:40 pm
by Mia Navarro 1D
When writing out the molecular formula BF3 + :NH3 --> NH3BF3, why does one draw the two dots next to NH3 reactant?

Re: Lewis Base Shorthand  [ENDORSED]

Posted: Mon Oct 30, 2017 1:43 pm
by Chem_Mod
The two dots represent 2 unpaired electrons on the nitrogen. Remember that there must be 8 valence electrons, in which 6 (2 per bond) are with the H, and 2 are with the N. This gives the nitrogen in :NH3 a formal charge of 0. (5-3-2=0)