Dominant 7 Chords
Dominant Seventh chords are played by adding the flat (♭) 7th note from the major scale to a major or minor triad.
Dominant Seventh Chords are popular in blues music because of their naturally bluesy sound. Minor Dominant Seventh Chords have a sad tone or sound.
Major 7th Chords
Major 7 chords are played by adding the major 7th note of the major scale.
Major Seventh Chords have a more romantic sound compared to Dominant Seventh Chords. Minor/Major Seventh Chords are used commonly as passing chords and do not necessarily have a sad or happy sound.