Half the periodic table needed by one fragrant substance (5)

I believe the answer is:

elemi

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'fragrant substance' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for elemi that I've seen before include "aromatic resin" , "Resinous stuff" , "Fragrant resin used as incense - Emile (anag)" , "It's fragrance" , "Extract" .)

I've seen this clue in The Independent.

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