This list has been truncated:

SDM, LMNM, RN, RHDM, NDM, TN, SMM, LD, RDM,...

Supply exactly one missing member - there are a few to choose from.

Looks like a series of elements missing their vowels:

SDM -> Sodium

LMNM -> Aluminum

RN -> Iron

RHDM -> Rhodium

NDM -> Neodymium

TN -> Tin

SMM -> Samarium

LD -> Lead

RDM -> Radium

So a possible missing member would be CRBN -> Carbon