I am using a crystal:
Now I always learned that crystals need capacitors, ceramic resonators do not. However, one of the things I look at if it needs it or not, is wether or not the crystal/resonator needs to be connected to ground, as I figured the ground is only needed for internal capacitors.
so in the case of this crystal, do I need one or not? as a ground needs to be connected.
Now I always learned that crystals need capacitors, ceramic resonators do not.
I suspect this is an over-simplification - from what I've seen, "crystals" are generally just that - bare crystals in a more usable package; "ceramic resonators" on the other hand generally come with the load capacitors built-in (at least in my experience), but I wouldn't state that as a general fact for all resonators. The DigiKey parametric search even has a "capacitance" field for the resonators section.
As noted already, the requirement for load capacitors is due to the application (e.g: oscillator), and is not an intrinsic requirement for the crystal or resonator itself.
The best way to determine if they're built-in or not, is to check the datasheet... the AWSCR-CPLA family of resonators for example (plucked from the top of the DigiKey section) includes the following information: specs, part number, equivalent circuit.
[...] wether or not the crystal/resonator needs to be connected to ground
This is going to be much more related to sheilding and mounting than whether a capacitor is required.
The ground is to shield the case, just as you might want to ground the 'can' on any crystal.
Whether you need to add capacitors or not depends on the application. Some chips might have integrated capacitors that are close enough.
But in most cases you would have to calculate the appropriate load capacitors for the crystal and for your layout and add them externally, probably about 15pF for this particular crystal (specified as 10pF load capacitance) and a good layout.
It's up to you to provide that equivalent load capacitance for the crystal, otherwise you may not get a frequency that is within the guaranteed limits, or, in the extreme, the circuit may fail to oscillate at all. It may fail to oscillate or start anyway, but that's more of a system problem.
Things in the datasheet that are your responsibility:
