why did Mendeleev place Tellurium before iodine even though Tellurium has a higher atomic mass than iodinde. Use term periodicity to explain

How many atoms are in 1.4 mil of phosphorus trifluoride (pf3)

Based on the equation and the information in the table, what is the enthalpy of the reaction?

Silver tarnishes as silver metal reacts with hydrogen sulfide, h2s, in the air. in this reaction, dark silver sulfide, au2s, covers the surface of silver. when silver is polished, this coating of silver sulfide can be removed from the surface. this makes the silver shiny again. enter the coefficients that balance the tarnishing reaction equation. (type 1 for no coefficient.)