Element of choice: Hydrogen
Why?
By controlling Hydrogen I can control when it will bond and what it will bond to. A little synthetic chemistry will tell you that controlling when Hydrogen Protonates or Depronates a molecule and/or when Hydrogen changes the nearby pH will grant control over altering that molecule.
But it doesn't stop there.
Elements differ based on the number of Protons. H+ is a Proton. Control over Hydrogen allows me to create isotopes of any element I want.
So with control over Hydrogen I have the ability to synthesis anything I could desire and slowly transport it.
Note: All of this merely assumed telekinetic control of Hydrogen Atoms. No control of other elements needed and yet I still can control compounds using the power of Hydrogen.