In a minor key, e.g. E minor, if you take the dominant triad, it contains the leading note. Is the leading note of the natural minor or the major for the dominant triad?
So for E minor dominant triad is it (B,D#,F#) or (B,D,F#)?
Strictly speaking, the notes of E natural minor are:
E F# G A B C D E.
So, if you want to use notes only from that scale, the chord would be
B D F#.
But in almost all the genres of music (even pop), it is really really common to borrow chords from other scales. In your example, you could borrow the dominant ( V ) chord from the E major scale (or the E harmonic minor or the E melodic minor), where the chord would be
B D# F#.
People often choose to borrow the major dominant chord, because the V-i relationship is a pretty strong one that defines your key, but the v-i (with the minor chord) isn't that strong. It isn't wrong, so if you like it you can freely use it.
It really depends on what you want to do. Both of them are correct. They differ on the sound outcome, because
B D F# is a minor chord whereas
B D# F# is a major one.
The term "leading tone" is equivalent to "scale degree seven of the major key." This doesn't mean that it's only found in a major key, just that it's the same pitch as the pitch that is scale degree seven of the major key. It is always a diatonic half step below tonic. In E minor, the leading tone is D-sharp.
Meanwhile, scale degree seven of the natural minor is determined by the key signature. E minor has only one sharp (F-sharp) in its key signature, so scale degree seven in E natural minor is D-natural. (We also call this the "subtonic.")
Meanwhile, there's another minor scale that we call "harmonic minor": this is a natural minor scale where you raise scale degree seven, thus using the leading tone instead of the subtonic. We call it harmonic minor because the leading tone allows us to create one of the most important harmonies in all of tonal music: the (major) dominant triad!
So, quiz time:
What's the subtonic of D minor?
C-natural. The subtonic is found in the natural minor, so use the D minor key signature (one flat, B-flat).
What's the leading tone of F minor?
E-natural. The leading tone is not found in the natural minor key signature, so we can think of it either as scale degree seven in major, the raised seventh scale degree of natural minor, or as a diatonic half step below tonic. We'll get the same answer all three ways.
The leading note is the seventh degree of the major - and minor - when that note is one semitone below the l, tonic, or root.It's called leading as it suggests a tendency to rise to the tonic next. However, it loses that propensity when it's lowered, as in some minors, and subsequently gets called the 'flattened leading note'.
If you're wondering which one to use, that's a different matter. More often, say, in Em, the D# is used, as it comes over as far more definitive, but take a song like Black Magic Woman, and the D (if it's in Em) is heavily featured. There are many minor blues which also go that way, too.
To make the chord on a B, then either works - use ears- so, B,D#,F#,A, or B,D,F#,A.
The D# features in the harmonic minor, and also the classical melodic minor, rising. The D features in the natural minor and the descending melodic minor, although jazzers prefer D# both ways. In the E minor key, of course!
An interesting dominant chord sometimes used in a minor key is the so-called Hendrix chord. 7#9. It has the major third in it, but also contains the sound of the minor third, labelled as #9. Thus a glorious clash of the two. If you can't decide which third to use, play 'em both!
Here are the triads in e natural minor:
However, minor dominant triads could not lead to the tonic smoothly and strongly. So we must use the harmonic minor in order to make a smooth lead to the tonic. In harmonic minor, we must raise the 7th degree note.
In fact, in e minor, we get these triads when the 7th degree note is raised:
Hope it helped!