An arpeggio is essentially a chord that is broken apart, playing one note at a time. We usually play them with a regular note-duration or rhythmic pattern. For example a C major chord may be played:
C -E G -C- E-G-C, arpeggiating the chord through two octaves and finishing on the tonic note.
We also see piano arpeggios in a repeating pattern as a method for sustaining the sound of the chord over several beats, or even measures. This compositional technique is called an ‘Alberti Bass’ which is usually, but not necessarily, played in the left hand. For example, imagine the following in steady eighth-notes:
C – G – E – G -C – G – E – G
Many Classical period piano works utilize Alberti Bass techniques.
To practice piano arpeggios, start with major triads and play them hands separately over two octaves. Use a simple 1-2-3 fingering for the right hand, and 3-2-1 fingering for the left hand employing basic thumb under and finger-over techniques. Work your way up to playing these chords both ascending and descending without stopping, hands together. Once you are confident with two octave arpeggios, begin to practice them up to four octaves with a metronome.
Cycling through the circle of fifths can be a way of quickly practicing all the major triads in just a few minutes. As a reminder, the roots for the descending cycle of fifths starting on C are:
C, F, B-flat, E-flat, A-flat, D-flat, F-sharp, B, E, A, D, G
After developing some confidence with major triads, add minor triads to your practice. A minor triad has a lowered third, compared to a major one. It is also the tonic triad of a minor key. For example, an A minor triad is the tonic triad of the A minor scale: A – C – E.
Most piano students also practice dominant seventh chords as piano arpeggios. Since they are four-note chords you will have to adjust your fingering to 4-3-2-1 and 1-2-3-4 for the left and right hands, respectively.
One final standard chord that students practice is the diminished seventh chord. Technically speaking, there are only three different diminished seventh chords:
C, E-flat, G-flat, B-double-flat
C-sharp, E, G, B-flat
D, F, A-flat, C-flat
You will find it useful, however, to consider all possible roots of these chords through enharmonic spellings. For example the first diminished seventh above is enharmonically equivalent to the one on A: A, C, E-flat, G-flat. Here we are reading the B-double-flat as an A. Another enharmonic reading of this same chord is: F-sharp, A, C, E-flat, where the G-flat is reinterpreted as F-sharp. The western system of musical notation is full of these kind of equivalencies.
There are several reasons why pianists should practice piano arpeggios. Like scale exercises, they have been traditionally incorporated into the student’s practice as a way to build strength and basic piano technique. Any technique that you need to work on can be done through practicing scales and arpeggios. Practice for speed, accuracy, tone and articulations. You can also work on your finger independence by playing them in contrary motion, or starting on different inversions in the two hands. Another common exercise is to play a scale in one hand while playing an arpeggio pattern in the other.
Practicing arpeggios is also great for building your reading skills and understanding of harmony. You could cycle a common chord progression though different keys with arpeggios to really become familiar with its sound. All of these practices will contribute to your development as a well rounded musician.