Your resources of SPM Chemistry and STPM Chemistry
As in your video, to allow the electrons from valence band to excite over conduction band, what do you mean by valence band and conduction band? To let the valence e get excited and become delocalised?
Oh. This is in Semester 1, when you learn about metallic bonding, and explaining Valence Band Theory. For more information, please googld Valance Band Theory