Drawing Electron Dot Diagrams

Electron Dot Diagrams, or Lewis Diagrams are... cool. Lemme show you why:

 LEWIS DIAGRAMS FOR SINGLE ATOMS

When Drawing Electron dot diagrams, the nucleus is represented by the atomic symbol.

For example:   Cl            Na

Determine the number of valence electrons (meaning the electrons in the outermost shell). Represent these by drawing that amount of dots around the chemical symbol.

Keep in mind:

*There are four orbitals (one on each side of the nucleus) and each can hold a max of 2e
*Each orbital gets 1e before they pair up

For Example:
Chlorine atom has 17 electrons.
2 in the first shell

8 in the next.

And 7 in the outer shell.

LEWIS DIAGRAMS FOR COMPOUNDS AND IONS

In covalent compounds, electrons are shared

First, determine the # of valence electrons for each atom int he molecule

Then, place atoms so that valence electrons are shared to fill each orbital

Examples:

Here is a VERY common covalent compound, H20... water!
Oxygen originally has 6 electrons, while each Hydrogen has 1 electron.

This totals up to 8 electrons, which fills up oxygen entirely as well as hydrogen (which only requires 2 electrons each, since its the first shell!)
 

And children, that's an example of how we share!

DOUBLE AND TRIPLE BONDS
Sometimes the only way covalent compounds can fill all their valence levels is if they share more than one electron (hence the double and triple!).
Examples

Carbon has 4 electrons, while each Oxygen atom has 6 in their valence shell.
This means that there's a lonely electron in each of the oxygens, and 2 lonely electrons in the carbon atom... so why not pair up and form a double bond?

IONIC COMPOUNDS

In Ionic compounds. electrons transfer from one element to another.
First, determine the number of valence electrons on the cation (positive ion) and move these to the anion (negative ion)
Then, draw [ brackets ] around the metal and non metal
-Write the charges outside the brackets
Par example,

Aluminum is a charge of +3, and Chlorine has a charge of -1. Since the electrons are moving onto the chlorine (we know this, since chlorine's negative), we only draw the electrons around the chlorine.
Remember to write the charges on the outside of the brackets!

POLYATOMIC IONS
First ,determine the # of valence electrons for each atom int he molecule

Then, subtract one electron for each positive charge OR add one electron for each negative charge
Example

CO3 -2

Carbon- 4 electrons

Oxygen- 6 electrons x 3 = 18 e

+2 electrons (because the charge is -2)