Carbon, hydrogen and metals: I turn them into gold (9)
I believe the answer is:
alchemist
'them into gold' is the definition.
I can't tell whether this defines the answer.
'carbon hydrogen and metals i turn' is the wordplay.
'carbon' becomes 'c' (C is the chemical symbol for carbon).
'hydrogen' becomes 'H' (chemical symbol).
'and' says to put letters next to each other.
'turn' indicates an anagram.
'c'+'h'+'metals'+'i'='chmetalsi'
'chmetalsi' anagrammed gives 'ALCHEMIST'.
(Other definitions for alchemist that I've seen before include "Seeker after gold" , "he sought a panacea" , "One seeking to produce gold, elixirs etc" , "His hope to discover elixir of life" , "Early experimenter" .)