SN2 Reaction help

Ok so I was watching a video tutorial about SN2 reaction but one thing is bugging me. In the video, the molecule (nucleophile) that is replacing the leaving group, only part of the molecule does it i.e. in NaCl, just the Cl substitues the leaving group but I've looked on other websites and it shows that the whole molecule, NaCl, substitues the leaving group.

Here's a picutre: Sorry for the bad quality, drew it in paint



Which one is correct, the first mechanism or the second mechanism?

Thanks

Aryl halides don't undergo SN2 mechanisms which is probably why you are getting confused.

eh?? This isn't an aryl halide.

JM has got it right.

he generally does, tbh

Two things....

1. this alkyl halide doesn't undergo Sn2 efficiently, Sn1 is probably the dominating mechanism.
2. NaBr doesn't exist as a discreet molecule. In a solid it is a collection of many (being stupidly large numbers) bromide and sodium ions in a crystal. In solution the crystal breaks down to form sodium and bromide ions in solution which are solvated by the solvent so that they only interact weakly with other ions. The reactive particle in this (ignoring that Sn2 most likely doesn't occur) Sn2 is the Bromide ion in solution, not a NaBr moleucle.

How come in this reaction: the whole molecule replaces the leaving group as apposed to just the Oxygen?

How come in this reaction: the whole molecule replaces the leaving group as apposed to just the Oxygen?