please explain it...
You still need to introduce different behaviours of different metals. In this first attempt, junctions of identical materials would give a current, which doesn't happen. More, the loop has two paths from hot to cold, which can't behave identically if you're to observe a current or voltage.
Beware also that electrons in a metal don't resemble a gas. For some properties maybe, for others not at all - for instance the heat capacity of a metal.