The 7th Chord adds another tone to the major triad chord. As the name implies the added tone is 7 steps from the root (following the scale). These chords are also called dominant chords and they are especially common in blues.
7 (dominant) chords
None for the moment in this category
These chords should not be confused with the maj7 and m7 chords.
Barre chord shapes
The chord illustrated above is open chords (except the F7), but they could of course also be played as barre chords. The shapes for dominant 7th barre chords looks like this:
The diagram to the left depicts an E-shape barre chord for dominant 7th and the diagram to the right depicts an A-shape barre chord (the lowest string should not be played) in the same chord group. They are moveable.