1. Why do chemical bonds occur?
>> They occur because there is an attraction of opposite charges. <<
That's part of the reason. Basically, it's a matter of stability. Two hydrogen atoms individually each with one unpaired electron. When an H2 molecule forms, the negative electrons can 1) interact with two positive nuclei instead of just one, and 2) pair up. Both of these outcomes make the H2 molecule more stable than two isolated H atoms.
The same principle applies when there are many electrons. The octet rule is a big factor. When an oxygen atom combines with two hydrogen atoms to form a water molecule, the oxygen has 8 valence electrons around it just like the noble gas neon. Meanwhile, the hydrogen atoms now have two valence electrons "around" them just like the noble gas helium.
2. Lewis dot structures of atoms.
Br 
Ca Kr
3. Lewis dot structures of molecules. (Good job with the dots!)
HCN There is a triple bond between the C and N atoms, and a lone pair on the N.
CH3Br
BrCl This is bromine monochloride, an "interhalogen" molecule. Its dot structure will be just like F2, Cl2, Br2, or I2.
CF4 OF2 H2O C2H6
4. Draw the structural formula for
NH3 CBr4 O2 H2S
CS2 This molecule looks just like CO2 (has two double bonds)
N2H4 Cl2 This is molecular chlorine, not a carbon and two iodines!! 
Steve
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