Spelling chords in keys
Write a triad and its inversions in any key with the right accidentals.
Triads on the degrees
On every degree of a scale you can build a triad from the notes of that same scale, skipping one note each time, in thirds. In major their qualities are always the same:
Degrees Triad
I, IV, V major triad ii, iii, vi minor triad vii diminished triad
In natural minor the order shifts: i, iv and v are minor, III, VI and VII major, ii diminished.
The triads on every degree of C major
Practice: Build triads
The key supplies the accidentals
To write the triad of a degree in any key you don't need to count semitones. Take the degree, add the next two notes skipping one each time, and apply the key signature: in D major F and C are sharp, so the triad on V is A, C♯, E.
Inversions use the same notes: the sixth chord on IV in D major is B, D, G.
D major: I – IV – V – I with the key signature
To find the degree of a chord, first find its root (stack the notes in thirds), then count the degrees from the tonic of the key.