Either I am so slow or everything goes very fast. Yes I am talking about how we can just come through 1.8 at first course of the term. Well it was not a disaster but let be honest I am not prepared for this much. Anyway, I am entering, and evaluating my lecture notes now.

Download the image for magnifying it.

I just want to add a few things in order to make this complete.

You can examine the experiments from here more carefully, no need to dig deep. 

Also about formal charges, lecturer said that halogens double bonded structure may appear as resonance structure but they are not real actually, just make people imagine the structure of given molecule more easily. And gave some of the anions and cations' names , at the table. At formal charge +1 column, first carbon with three bond and nothing else names as carbocation, and at formal charge -1 carbon with three bonds and a lone pair named as carboanion. And this one

Carbon may have disobedient structures to octet but oxygen can not have. And we stopped here.


Nucleophilic Substition and Elimination Reaction

First of all I want to say something, here I will mention 4 different reactions ( SN1, SN2, E1, E2). They are theoritically always competitive to each other. But not in all situations. So only after learning them one by one, you will grasp the issue , not before. Be patient ;)

Here in first image, C is just carbon and Ss are a substition. LG is a better leaving group than substitions and Nu: is nucleophile. Yes, we should first learn what the hell they are before entering the reactions.

Carbon is an element which can make up to four bonds to achieve octet ( having 8 electron at outermost orbital (oct = 8)

LG is a leaving group, which have many electrons on it and can be stable in anionic state in corresponding solution. Basically we can just seperate LG from C with electrons of sigma bond between them on LG. 

Nu: is a nucleophile which is electron rich and can react with electrophilic centre ( which has electron deficiency ). 

Electrophilic centre : Here it is carbon, because of LG's electronegativity, it has lower electron density on itself and can be assumed electron deficient; and so, electrophilic centre.

Substitions simply binded with C covalently but not has much electronegativity like LG, so breaking that bond is harder, and even impossible by nucleophilic substition or elimination reactions. 

So there were definitons. And now think about the image on top of this text. There are electron rich groups and and electron deficient group. In Lewis Acid-Base definition, electron rich can be classified as base and deficient one is acid. So there merely be acid-base reaction. But there is another Lewis structure rule that Carbon can not make 5 bonds, which extends 8 electron to 10. So the most possibly leaving group will leave the structure. And it will be LG because it is stable in solution with anionic structure and its bond with C is easier to break among the other substituents. But there is one very crucial spot : A nucleophile is not a computer program, just like any other atoms & molecules. It just collides every time with every angle to our carbon containing molecule, but because of electron density of other substituents and leaving group, it just jumps back. Only when nucleophile reach to molecule at opposite direction of the leaving group (effective collision ) it may make LG leave and settle at its place and give product. 

To sum up, a nucleophile(here minus charged one) will be binded, it's electron density make others move away from them, and LG will be completely leave the structure. So there also be an inversion of configuration. (R from S or S from R ) . This reaction is named SN2 .