For the piano/composers: I compose music for the piano in my spare time, and one particular chord that has caught my attention (as one that I like a lot) is the D-F-G chord in C Major.
I have seen Mozart use this chord many times. In particular, his piano sonata in C (No.16 K.545). In both the first and second movements, he uses this chord at the beginning. In the first movement, he plays the I chord, then quickly switches to D-F-G, then back again. I don't know what that chord is. If I had to guess, I would say that it is a V7 chord second inversion without the 3rd? (D-F-G-B, excluding the B). In the second movement, you can see the same thing except in the key of G Major.
Link to the Music Sheet: Sonata in C Sheet Music
What interests me most about that chord in particular, is that it doesn't seem like a full chord change. It seems as though Mozart uses it in the middle of the I chord. It seems like some kind of composing "trick" to me. I have heard in the past about how it is possible to extend chord progressions by switching back and fourth between two chords. For example, ending with V, I, V, I [...] rather than just V, I. Perhaps Mozart was using a technique of some sort to lengthen the I chord and keep it interesting?
And as a last question about the "D-F-G" chord: Is there a particular name for a chord like that? I know that a Csus4 is C-F-G, and Csus2 is C-D-G. I had some thoughts that maybe D-F-G might really be some kind of ii chord variant.