Chemistry Review Chapter 16: Ionic Bonds (Lewis Dot Structures, Shapes, Imf, and Polarity)

Steps to Drawing Lewis Dot Structures Example: CO3 2- 1. Count the number of valence electrons for the molecule (CO3 2- = 22) 2. Find the central atom by locating the least electronegative element with the exception of Hydrogen which will always go on the outside. (In this case carbon is the least electronegative) 3. Place the central atom with all single bonds to the attached atom. 4. Place electrons on all attached atoms to make them have an octet 5. Double check that the number of electrons matches that number of valence electrons in step 1 and that all atoms have an octet 6. If you do not have enough electrons add more to the central atom. 7. If you have the right number of valence electrons but the central atom does not have an octet add double and triple bonds.

Shape and Bond Angle Remember it is all about the number of attached species to the central atom vs the lone pairs (lone pairs count as attachments) 2 attachments is always linear 180 degrees 3 attachments none of which are lone pairs in Trigonal Planar 120 degrees 3 attachments with one lone pair is bent triatomic still 120 degrees 4 attachments no lone pairs is Tetrahedral 109 degrees 4 attachments 1 lone pair is pyrimidal (VSEPR theory: bond angle decreases by 2 degrees) 107 degrees 4 attachments 2 of which are lone pairs is Bent 105 degrees due to VSEPR

Polarity 1. Unequal Sharing of Electrons 2. Based on the fact that some elements are more electornegative than eachother 3. Think of it like tug of war…if electrons are being pulled, but equally in all directions it is non polar IE CH4 4. It is based on electronegativity (so remember the trend) and shape (important to know Lewis dot structures)

IMF (Inter-Molecular Forces of covalent molecules) 1. How the individual molecules interact with each other (IE all the H20 molecules in a glass of water 2. London-Dispersion Forces is caused by the movement of electrons and occurs in Non-Polar molecules, They are also the weakest forces. They increase witht the size of the molecule (C4H12 has much more london dispersion forces than CH4) 3. Dipole-Dipole forces are stronger than London Dispersion Forces, but are still not the strongest. They are created by the alignment of the positive and negative “poles” of the molecules (IE H2S) 4, Hydrogen Bonds are FON! These are much stronger forces that are similar to Dipole-Dipole but are much stonger due to the extreme electronegativity difference between Hydrogen and the three most electonegative atoms (F, O, N)

Order of Increasing IMF (Weakest)London Dispersion<Dipole-Dipole<Hydrogen Bonding<Ionic Bonding< Network Covalent Bonding (IE Diamond) (Stongest)