To expand your chordal vocabulary, let’s start with dominant seventh chords. These chords include the flatted seventh of the respective key, thus consisting of the root, third, fifth (the major triad) and flatted seventh. You can find the flatted seventh by moving down two half steps from the root. In the key of C the flatted seventh is B♭ (two half steps down from C), in the key of F it is E♭ and in the key of G it is F and so on.
Dominant Seventh Chords (with the seventh marked in blue)
If you add these notes to the chords, you will get a bluesier sound, because dominant seventh chords are very common in blues and jazz. Because of the importance of these seventh chords for musical styles such as blues, jazz, funk, soul and gospel, they should be on your list of essential concepts to master on the piano. Dominant seventh chords are written as dom7 or mostly just 7.
The following riff gives you a taste of the bluesy sound of dominant seventh chords. The F7 and G7 chords are played as inversions with the the top two notes moved down an octave.