B Mixolydian — 7th chords
Four-note stacks of thirds on each degree — root, 3rd, 5th, 7th. The added 7th gives jazz, gospel, and modern classical voicings their distinctive colour.
All 7 seventh chords in sequence
Degree 1 · I7B7
Degree 2 · ii7C#m7
Degree 3 · iii°7D#m7b5
Degree 4 · IVmaj7Emaj7
Degree 5 · v7F#m7
Degree 6 · vi7G#m7
Degree 7 · VIImaj7Amaj7