As the name suggest, extended piano chords extend beyond the range of the major scale. Recall that chords are created with respect to there corresponding scales. For example, the major scale of “G” has this 8-note sequence: G,A,B,C,D,E,F#,G.
Chords that require notes beyond the 8th note (e.g. the last “G”) are extended piano chords.
The 9th, 11th and 13th chords are extended chords and are very popular in jazz music.
Noticed that the notes are displayed on both the treble and bass staffs for these chords. This is because these chords generally require both hands to play them.
The ninth chord is just like the seventh plus the 9th note from the root (counting the root itself).
The eleventh chord is just like the ninth plus the 11th note from the root (counting the root itself).
The thirteenth chord is just like the eleventh plus the 13th note from the root (counting the root itself).