Hi Amalia,
This video specifically showed the nucleophilic attack effect which refers to the process in which a nucleophile, which is an electron-rich species, donates a pair of electrons to an electron-deficient site, typically a positively charged or partially positive atom (an electrophile). This interaction is fundamental to many reaction mechanisms, particularly substitution and addition reactions.
Each reaction video moving forward shows and explains these concepts inside the mechanism.
For example if the next reaction you cover is substitution (SN1 and SN2) reactions then you'll see that explained in these videos:
Replied on Lesson: Mechanisms Intro: Drawing Curved Arrows
02 Nov 15:51
Chemmunity Team
The loss of the leaving group is an essential step in many organic reaction mechanisms, particularly in nucleophilic substitution (SN1 and SN2) and elimination reactions (E1 and E2). A leaving group is an atom or group of atoms that detaches from the main molecule, taking with it a pair of electrons and thereby stabilizing the overall reaction.
A leaving group is an atom or a group that can detach from the parent molecule during a chemical reaction, leaving behind a reactive intermediate such as a carbocation or a negatively charged fragment.
The ability of a group to leave depends on its stability once it detaches; the more stable it is after departure, the better the leaving group it makes.
Alkyl Halides: Halides such as Cl, I and Br are common leaving groups due to their ability to stabilize the negative charge after they leave.
Water: In reactions where OH− is protonated to form H2O water becomes a good leaving group due to its stability in solution.