Ionic bonds happen when Metals give electron to non-metals and covalent bonds happen when Non-metals give electrons away. Knowing this:
-NaF = ionic (Na is a metal, F is a non-metal)
-NF3 = Covalent (N is a non-metal, F is a non-metal)
-SiF4 = Ionic (Si is a metalloid, F is non-metal)
-CaF2 = ionic (Ca is a metal, F is a non-metal)
-NH4F = covalent (N is a non-metal, H is a non-metal, F is a non-metal)
Hope this helps
The mechanism is as suggested
1) Protonation of alcohol
2) removal of water molecule to give carbocation
3) hydride shift to give more stable carbocation [rearrangement]
4) the stability of carbocation due to resonance
5) removal of proton and formation 1-phenyl-1-propanone.
This is Pinacole pinacolone rearrangement
Thus the reaction can be depicted as