Presentation on theme: "How To Draw Lewis Structures for Covalent Compounds Using CO 2 as an Example."— Presentation transcript:
How To Draw Lewis Structures for Covalent Compounds Using CO 2 as an Example
Calculate the number of valence electrons. –What is the electron configuration for each atom? C O2 – 6 1 atom of Carbon x 4 valence electrons each 2 atoms of Oxygen x 6 valence electrons each 1(4 e - ) + 2(6 e - ) =16 e - Red indicates valence electrons
Draw a skeletal structure Identify a central atom –Often the element that appears only once in the formula –Often carbon COO
Add electrons so that each atom has eight electrons Exception H, He, Li, Be, B Always do this step despite the number of valence electrons you calculated in step 1. COO
So now each atom has 8 electrons or dots C OO Central Carbon has 8 electrons
So now each atom has 8 electrons or dots C OO Left Oxygen has 8 electrons
So now each atom has 8 electrons or dots C OO Right Oxygen has 8 electrons
BUT There are a total of 20 dots or electrons. We need 16 dots or electrons. C OO We must add at least one double bond.
To share an additional pair of electrons and form a double bond, two pairs must be removed from two adjacent atoms and a pair must be shared between those atoms. C OO
C OO Now there are 18 electrons or dots. To get 16, add another double bond (share another pair of electrons).
To share an additional pair of electrons and form a double bond, two pairs must be removed from two adjacent atoms and a pair must be shared between those atoms. C OO Now there are 16 electrons. This is our final structure.
We often rearrange the electrons to show that they separate as much as possible from each other. C OO Now lets check that all atoms still have 8 electrons each.
OOC Final Structure
OOC 8 Electrons Around Central Carbon
OOC 8 Electrons Around Left Oxygen
OOC 8 Electrons Around Right Oxygen
OOC Final Structure
2 atoms More than 2 atoms
Bonding domains domain Domains
Now we can predict molecular shape and polarity for CO 2 How many bonding domains does the central atom have?2 How many nonbonding pairs or lone pairs or nonbonding domains does the central atom have?0 What is the shape from the table? Linear Bond Angle180 degrees OOC
Polarity Draw an arrow from the more electronegative atom(s) to the less electronegative atom(s). If the arrows point in one general direction, the molecule is polar. If the arrows cancel out the molecule is nonpolar. Be certain that the structure takes into account the shape of the molecule.