Lewis Diagram (Molecules)

Recently in class we have been learning structures of the Lewis Diagram.

Here's an example:


Mr. Stitt taught us a great way to draw the diagram that is easy for the class to remember.
First, here are the instructions.
1. Count up all the valence electrons.
2. Add or subtract electrons to account for any charges.
3. Put the least electronegative element in the center (except Hydrogen because it can only make one bond) and form one bound to out elements.
4. Complete octets (or duets in the case of Hydrogen around the outer atams first)
5. Create double or triple bonds to satisfy octects on the central atom.
6. If the entire compound is charged, put it in [ ] and place the charge on the outside top right corner of the bracket (ex: [ ]+)
7. Sulfur can actually acomodate 12 electrons (six bonds) and phosphorus can accomodate 10 electrons (5 bonds)

After you make your diagram, the best way to see if the lewis diagram was drawn correctly you have to check formal charges. To do this is to find one that is actually made by nature.
Ex:
(# of valence electrons on plain atom) - (# of valence electrons on atom in compound)

But you have to make sure you remember exceptions that are able to take place in the Octet Rule.
* Sulfur can have 12 electrons in it's valence (6 bonds)
* Phosphorus can have 10 electrons in its valence (5 bonds)
* Boron can have 6 electrons in it's valence (3 bonds)

These bonds are unusual but help the diagram work. When finding formal charges these bonds enable them to come out equal to nature.

Naming Compounds

There are three types of Compounds:

Type I: * Contains a metal that is in groups IA, IIA in periodic table or consist of the elements Al, Zn, Cd .   
            * Dont change the name of the cation
            * Change the ending of the anion to "-ide"
            * Never change the name of any polyatomic ions.

Type II: * Contains a metal that is NOT in the groups listed above or consist of the elements.
             * Determine charge on the cation (balance the total anion charges)
             * Don't change the name of the cation and put the charge of the cation after its name.
             * Change the ending of the anion to "-ide"
             * Never change the name of any polyatomic ions.

Type III: * No metals or polyatomic ions.
               *Name each element with prefixes
               * Don't use "mono" of first element
               * Change ending on last element to "-ide"

This are the procedures you take while making formulas.

Ionic Compounds

Do you know what an Ionic Compound is?
Well as you may know; ion- a charged ion.

There are two different charges that consists with these Ions known as; Cation and Anion.
I was taught a special way to remember with has a positive and negative charge.

(Cation)                                        (Anion)
Ca- + - ion                                    A - N -ion
a                                                          e
l                                                           g
l                                                           a
e                                                          t
d                                                          i
                                                            v
                                                            e

These charges play a large role in a method called "The Criss Cross Method."

You have your formula with charges included, then you must do the criss cross method to balance the formula.

Ex:                Na+1    N-3
     C.C.M. :  Na3      N

See how you use the charges to balance the equations?