Hello --
The "chordal seventh" is going to be different depending on the chord you're talking about -- I believe the "chordal" just tells you that you're in the context of a chord (instead of in the context of your key signature and scale).
So if you are building a V7 chord in C major, the leading tone in C major (the seventh
scale degree) is B.
The "chordal seventh" for the V7 chord is F, since the V7 chord is G B D F. This note, the chordal seventh of the V7, is usually resolved down to the E (3rd scale degree) when V7 resolves to the tonic chord.
Does this help? If you are building a seventh chord based on the tonic chord in the scale, for example the major-major seventh C E G B,
then the chordal seventh is the same as the leading tone for the scale.
-Rob