Does arcing occur if nothing is plugged into the outlet?
Arcing - electrical current flowing across an air gap - only occurs when there's an electrical potential - a voltage - between the material on either side of the gap.
You can get arcing in loose electrical connections, such as between the wire loop and the screw terminal on a receptacle.  This is considered a series arc - the gap is in series with the circuit.
A series arc will only occur in your example when there's a potential between the screw and the wire.  There is only a potential present if there's a load on the circuit - when something's turned on and running.
A parallel arc could occur when there's nothing plugged in.  If there was weak contact or near-contact between hot and neutral in the box that would create a parallel arc.  That can happen with a skinned hot wire touching the metal box, for example.  (If the contact is reasonably solid, there would be no air gap, and it will create a dead short, which should trip the breaker or blow the fuse quickly.)