This episode outlines the Diatonic chords–the ones that fit with no added sharps or flats–within a key. 

In a Major key we have 1, 2m, 3m, 4, 5, 6m, 7dim.

In a Minor key we have 1m, 2dim, 3, 4m, 5m, 6, 7.

In Harmonic Minor we raise the 7th note of the key by a half step creating a LEADING TONE: 1m, 2dim, 3, 4m, 5*, 6, #7dim.