Montevideo: Solution

As hinted by the example (4112 → fluoxetine aka Prozac), look up the numbers in the Merck Index (12th ed.) They all reference either single elements or 1:1 compounds of two distinct elements.

Take the atomic number of each element and index into the alphabet. Random anagramming gives the answer FREQUENCY.

808Argon Ar 18 R
1345Boron B 5 E
1345Boron B 5 E
5405Lithium ChlorideLi/Cl3/17CQ
5604Manganese Mn 25 Y
8348Scandium Sc 21 U
8439Silicon Carbide Si/C 14/6NF