piano scale
F major
F1G2A3B♭4C5D6E7
The seven-note scale everything else is measured against: two whole steps, a half, three whole steps, a half.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
FWGWAHB♭WCWDWEHF
What is true of it
F major is F, G, A, B♭, C, D and E, and back to F.
Its steps are W – W – H – W – W – W – H, where W is a whole step and H a half.
On the same tonic, F melodic minor differs from it by exactly one note.
Chords made only of these notes
CmajorC7dominant seventhDmminorDm7minor seventhEdimdiminishedEm7♭5half-diminished seventhFmajorFmaj7major seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.