Lewis Dot Structures

Background: Lewis dot structures G.N. Lewis, at the University of California at Berkeley devised a simple way to understand the nature of the chemical bond in both ionic and molecular compounds. His method rests upon focusing on the valence electrons of the elements. He represents these valence electrons as "dots" around the four sides of the elemental symbol.

Steps to Drawing Lewis Dot Structures 1. Count all of the electrons in the valence shells of all atoms in the molecule. Sometimes it helps to draw the symbols with valence electrons shown. You should write the total # of valence e- down.

Steps to Drawing Lewis Dot Structures 2. Arrange symbols on the page so that each atom is adjacent to all other atoms to which it is covalently bonded. It’s important to keep in mind how many bonds each one can make. Carbons usually central because they form 4 bonds. Hydrogens & halogens can only form 1 bond. C, O, & N can form multiple bonds.

Steps to Drawing Lewis Dot Structures 3. Draw a line representing a bond between all atoms that are bonded together. A line = 2 electrons!

Steps to Drawing Lewis Dot Structures 4. Most atoms are surrounded by 8 electrons (full valence shell). This is called the octet rule. Electrons can be placed into the molecule as pairs around an atom, or in bonds (including double and triple bonds). Keep adding until each atom has an octet or there are no more electrons available (your total is at the total you counted in #1).

Steps to Drawing Lewis Dot Structures 5. If you have placed all available electrons around atoms in the molecule and do not have octets for each, it is important to check to see if you have maximized the sharing of electrons in double or triple bonds.

Example Lewis Dot Structure Draw the Lewis Dot Structure for CO2 1. Count the total valence electrons: C = 4, O = 6, O = 6 Total = 16 Individual Lewis Dot Structures of atoms:

Example Lewis Dot Structure Draw the Lewis Dot Structure for CO2 Total Valence e- = 16 Carbons are usually in the middle, so I would start with O – C – O This picture has 4 e- in it so far (each bond = 2), so I need 12 more e- total.

Example Lewis Dot Structure Draw the Lewis Dot Structure for CO2 Total Valence e- = 16 (pic from last slide needs 12 more e-) The octet rule should be filled for each atom (surrounded by 8 electrons), so I would start adding dots to fill them O – C – O These all have full octets now, but my total e- is 20, and I need it to have 16.

Example Lewis Dot Structure Draw the Lewis Dot Structure for CO2 Total Valence e- = 16 Since this structure has too many e-, there must be a double bond. Also, remember C forms 4 bonds, O forms 2 bonds…. In this one, each octet is filled, and each atom forms its’ ideal # of bonds. And most importantly, it has 16 valence e- (like you counted).