Arpeggios and scales differ in their construction and purpose. Scales are the building blocks for chords, melodies, and improvisation. They are made up of a specific combination of notes that can be used to play over any chord. The major scale is the most commonly used and contains seven different notes (1-2-3-4-5-6-7).
A scale can also be major or minor, depending on where you begin. An arpeggio is simply a series of notes played one after the other in a chord. They can be played in many different ways (ascending or descending), by using only certain notes from a chord or even with other notes added in.