Using valency to stretch Year 7

In his recent article Peter Nelson¹ argues that teachers should use of the concept valency to underpin the electronic theories of bonding that are taught in GCSE level chemistry courses. I would argue that we should use these concepts even earlier. 

In my experience as a secondary school chemistry teacher, the electronic theories of covalent and ionic bonding are perhaps the first time pupils meet the concept of bonding in depth. At Key Stage 3 pupils would have been taught bonding in terms of rigid sticks between atoms that can be broken and reformed in chemical reactions. Furthermore, teachers provide little experimental proof to illustrate how the electronic theories of bonding originated, resulting in a 'you will just have to trust me on this' approach. The intellectual leap (of faith) we are asking students to make on this topic as they move from Key Stage 3 to Key Stage 4 is enormous.