Electron Dot Diagram and Structural Formulas

[JDK]

Hello,

I was hoping someone here might be able to explain to me how to determine electron dot diagrams and structural formulas of diatomic/polyatomic elements and compounds. For example...

Nitrogen Tri-iodide ( NI3 )

I know the basics of electron dot structures, but when the atoms start having double covalent bonds I lose track and get confused. Structural formulas are also unclear to me except for that they are a simpler version of the dot diagrams using a single line for single covalent bonds, double for double covalent, and so forth. Thanks a bunch.

 

[thunderfvck]

It really isn't that hard. I remember when I first really started having to draw structures with the whole lewis dot deal I had a bit of trouble doing it.
First thing you have to consider is the valence of the central atom, in your example it is nitrogen. Nitrogen has a valence of 5 electrons. And the bonding atoms are the iodines, and they have a valence of 7, so they only need one more electron to be happy.
So this is how to work out your example...

N has five valence electrons, 3 of which are going to be shared with the iodines (since there are 3 iodines), which leaves you with two left over. So those two are a lone pair, which is simply two electrons together. So you'd have the N with three iodines attached to it, sharing one of their seven valence electrons with one of the electrons from nitrogen. That makes three lone electrons from nitrogen as a total, one of each three being shared with one of the other electrons of iodine. And you have a lone pair sitting on the side of the nitrogen. It's really much easier to explain by drawing it but that's obviously not an option.
There are no double bonds involved here so this was a pretty easy example, but in the case of the double bond, let's look at CO2. Carbon has 4 valence electrons and oxygen has six, so each oxygen needs two electrons from carbon. So two of carbon's electrons are shared with an oxygen, and two of oxygen's valence electrons are shared with a carbon. Two dots on one side of carbon plus an additional 2 dots from oxygen makes four. These four comprise the double bond. The same goes for the other oxygen in CO2. So, counting the electrons around carbon, there are 4 on each side, two sides, making 8. There are two lone pairs on each oxygen plus the four involved in the double bond between carbon and oxygen; the two lone pairs make four electrons total plus the double bond makes eight. Everyone's happy.
So much easier to have a diagram.
I'm sure there are many sites online (google.com) that will have drawings to accompany the explanation, you should try doing some searching.
I hope I helped.

 

[JDK]

Hmmm. Well, going piece by piece here, I think I understand how you came to making a dot diagram of nitrogen tri-iodide. It would end up looking something like this... correct?

 ..  ..  ..
:I : N : I :
 ..  ..  ..
   :I :
    ..

...and the CO2 example would end up looking like...

  ..     ..
:O::C::O:

They look a tad bit rough.. I know.. but the meaning is implied well enough. I hope.

 

[thunderfvck]

Wow. Very nice
Yeah, that's exactly what I was referring to. Nice. Try finding more examples to practise online. eg. google!

 

[JDK]

Excellent. Thanks so much for your help. If I encounter any more problems in this area I'll be sure to post them in this thread again. Thank-you!