Describing some bonds slipping in value? Not yielding nothing (9)
I believe the answer is:
univalent
'describing some bonds' is the definition.
(univalent bond is a type of chemical bond)
'slipping in value? not yielding nothing' is the wordplay.
'slipping' is an anagram indicator.
'yielding' is a deletion indicator.
'nothing' becomes 'o' (looks like zero - 0).
'not' with 'o' taken away is 'nt'.
'in'+'value'='invalue'
'invalue' is an anagram of 'univale'.
'univale'+'nt'='UNIVALENT'
(Other definitions for univalent that I've seen before include "Capable of particular combination" , "Able to bond only once" .)