HOW TO DRAW LEWIS STRUCTURES! A STEP BY STEP TUTORIAL Kyla Smart Michael Burnette Nick Ryan Lor Ross Sison

So…what are Lewis Structures? Lewis Diagrams are used to describe the structure of covalent molecules. They use a simple and clear notation to represent the valence shell electrons of all of the atoms in a molecule.

How to Create a Lewis Structure Step 1. Add up the number of valence electrons present in all of the atoms in the molecule. To determine how many valence electrons an atom has you can use the periodic table. The number of valence electrons is equal to the group number of the element. Tip: To move faster you can multiply the group number of the element with the number of atoms of that element in the molecule

Example: Step 1 Assignment: Draw a Lewis structure of the molecule O 3 There are 3 oxygen atoms Oxygen is found in group 6 Therefore Oxygen has 6 valence electrons 3 X 6 = 18 There are 18 valence electrons in O 3

Step 2. Draw a rough structure Pick a central atom and connect the remaining atoms with a single bond to the central atom The central atom is usually the first atom in the molecule

Example Step 2. O-O-O

Step 3. Place dots around all of the atoms. These dots represent unpaired valence electrons A single bond accounts for 2 valence electrons Make sure that each atom has 8 valence electrons around it (there are a few exceptions to this rule such as Hydrogen)

Example Step 3. O-O-O Represents the valence electrons

Step 4 Count up the number of electrons present in the atom Each bond represents 2 electrons Check to make sure that this number is equal to the number determined at the beginning If it matches, then YOU’RE DONE If not, move on to step 5

Example Step 4. O-O-O There is a total of 20 valence electrons in this diagram. In step 1 we decided that there needed to be 18 valence electrons. This diagram has 2 extra valence electrons

Step 5 To lower the total number of electrons, take 2 electrons off of two atoms that are bonded together and place another bond between those two atoms. Each time you do this, it will lower your electron count by 2 Do this until the number of electrons is equal to the number determined in step 1. Make sure that the molecule is as symmetrical as possible. For example, do not have a triple bond and a single bond when you could have a two double bonds

Example Step 5. O-O=O Remove a pair of valence electrons from the central atom Remove a pair of electrons from one of the outer atoms The two atoms that you have removed the electrons from are now sharing, not one but two pairs of electrons and therefore are double bonded The diagram now has 18 valence electrons Congratulations, this number matches the number from step 1.

A Helpful Hint HONC Halogens/Hydroge n Oxygen Nitrogen Carbon This diagram can help you remember the number of bonds that each atom tends to form. Hydrogen & Halogens tend to form 1 bond Oxygen tends to form 2 bonds Nitrogen tends to form 3 bonds Carbon will form 4 bonds (with some exceptions)

Also… If your compound has a charge on it (aka is an ion), add up the total number of electrons present and either add extra electrons if you have a negative charge or subtract electrons if you have a positive charge Draw the structure of the compound so that the total number of bonds and lone pairs adds up to the correct amount of electrons Draw brackets to the left and right of the Lewis Structure and put its charge to the right of the top of the right bracket

Example NO 3 - O=N O O

YOU’RE DONE!