The difference between scales and keys
Scales and keys both refer to groups of tones and sometimes we can either say scale or key and mean the same thing. Still, there is an important distinction between them.
A key defines the tonal center and it is common to say that a piece of music is written in the key of… For example, a song that includes the chords G, C, D and Em is most likely in the key of G. That is because all the tones that belongs to the four chords also belongs to the key of G, which are G, A, B, C, D, E, F#.
Whereas G Major Scale includes the same tones (G, A, B, C, D, E and F#), a song in the key of G could at the same time include several scales. For example, a guitarist playing a blues song in the key of A may use both the pentatonic minor and major scales.
Another main difference is that keys are typically classified as major or minor. But with scales, there is a much larger diversity. While we often talk about major and minor scales, there are also pentatonic scales, diminished scales, bebop scales and lots of others. A pianist may choose to use the E flat Bebop scale in a jazz tune, but we don't say about a jazz tune that it is in the key of E flat Bebop.
Music scales can be seen as tools for creating melodies, harmonies and improvisation. Music keys, on the other hand, serve as a way to describe the overall tonal framework of a piece of music.
Appendix A
The name of all major keys and notes:
C Major: C, D, E, F, G, A, B
C# Major: C#, D#, E#, F#, G#, A#, B#
Db Major: Db, Eb, F, Gb, Ab, Bb, C
D Major: D, E, F#, G, A, B, C#
D# Major: D#, E# , F#, G#, A#, B, C#, D#
Eb Major: Eb, F, G, Ab, Bb, C, D
E Major: E, F#, G#, A, B, C#, D#
F Major: F, G, A, Bb, C, D, E
F# Major: F#, G#, A#, B, C#, D#, E#
Gb Major: Gb, Ab, Bb, Cb, Db, Eb, F
G Major: G, A, B, C, D, E, F#
G# Major: #, A#, B#, C#, D#, E#, F##, G#
Ab Major: Ab, Bb, C, Db, Eb, F, G
A Major: A, B, C#, D, E, F#, G#
A# Major: A#, B#, C##, D#, E#, F##, G##
Bb Major: Bb, C, D, Eb, F, G, A
B Major: B, C#, D#, E, F#, G#, A#
Appendix B
The name of all minor keys and notes:
C Minor: C, D, Eb, F, G, Ab, Bb
C# Minor: C#, D#, E, F#, G#, A, B
Db Minor: Db, Eb, Fb, Gb, Ab, Bbb, Cb
D Minor: D, E, F, G, A, Bb, C
D# Minor: D#, E# , F#, G#, A#, B, C#
Eb Minor: Eb, F, Gb, Ab, Bb, Cb, Db
E Minor: E, F#, G, A, B, C, D
F Minor: F, G, Ab, Bb, C, Db, Eb
F# Minor: F#, G#, A, B, C#, D, E
Gb Minor: Gb, Ab, Bbb, Cb, Db, Ebb, Fb
G Minor: G, A, Bb, C, D, Eb, F
G# Minor: G#, A#, B, C#, D#, E, F#, G
Ab Minor: Ab, Bb, Cb), Db, Eb, Fb, Gb
A Minor: A, B, C, D, E, F, G
A# Minor: A#, B#, C#, D#, E#, F#, G#
Bb Minor: Bb, C, Db, Eb, F, Gb, Ab
B Minor: B, C#, D, E, F#, G, A