Dominant 7th Chords

The dom7 chord is a major triad with an added flat 7th
scale degree. For example, the notes for a
C7 chord are C E G Bb. Notice that the note B is flat
where as normally in the key of C major you would
have a B natural note. This means that you are really playing
in the tonality of the key of F maj. or C mixolydian


This chord tends to resolve to a major or minor chord a fifth below
or a tritone up.


Adding the b7 creates a stronger
gravitational pull than just using a straight
major triad. Try playing a G maj to C maj,
and then G7 to C maj, notice that the 7th (the note F)
resolves to the 3rd of the C maj chord (the note E)


The tension in the dom 7th chord is created by the tritone
between the third and 7th which resolve to the root and 3rd
of the I chord in contrary motion. For example, the B and F notes
in a G7 chord resolve to the C and E of C maj.