A coil connectd to AC voltage source
the coil will resonate


To make a coil resonate it must be tuned with a capacitor so no, it is very unlikely to resonate


  the coil will resonate and radiate an electromagnetic wave.


At 7Hz there will be virtually no electric field other than what the AC voltage source is generating whether it connects to the coil or not.


  What's the frequency of the radiated wave and does it depend on the
  dimensions of the coil and its number of turns?


The frequency of the radiated magnetic field is the same as the frequency of the AC excitation, 7Hz. The frequency is fixed by the incoming AC and has nothing to do with the coil construction.