Note the octet rule is descriptive but lacks explanatory power.

Link to happy atoms in DauM https://www.rsc.org/cpd/resource/RES00001452/analogies-in-chemistry/RES00001448#!cmpid=CMP00003578

Why do hydrogen and flourine react? F2F sheet and video 

http://www.rsc.org/learn-chemistry/resource/res00001098/hydrogen-fluoride. A point to know here that this will introduce covalent bonding before we use it in the course BUT teachers also ignor this when using Na and Cl where only atoms of chlorie referred and the idea of chlorine exisiting as a diatomic molecule is ignorred. 

Also EiC article pointing Octet rules oK

 http://www.rsc.org/eic/2014/03/chemical-bonding-misconceptions-electrostatics

Could also develop the octet rule in the light of thermodynamics  for example by comparing the 1st IE of Na and 1st EA of chlorine. Then looking at the 2nd IE of Na nad 2nd AE of chlorine.