Aluminium

[potterfan3]

How does the structure of Aluminium make it a) impermable and b) odourless

[beso]

The highly stable oxide layer that forms on aluminium is of similar structure to the parent metal and clings tightly, sealing of the underlying metal.

A similar process makes stainless steel non-corrodable.

Metals that corrode have an oxide that is a different size to the parent metal causing it to crack off and expose more metal.

[Teddio]

Aluminium is odourless because it has zero vapour pressure and it and its oxide are non-volatile.
Aluminium is often anodized, a process which produces a relatively thick, hard coating of aluminium oxide on the surface. This may be dyed giving a coloured effect.
On the subject of smelly metals, look up Osmium.