The dominant 7 chord is simply the major chord with the b7th note of the major scale added.
Let’s use the C major chord to show this:
C Major
C7 (dom 7)
You can use MusicWheels™ to quickly identify dominant 7 chords by using the blue sector at the root note of the chord:
Dominant 7 Chord Formula:
A dominant 7 chord is made up of notes based on the intervals of the major scale.
The root note of the dom 7 chord is derived from the 5th note of the major scale.
The dom 7 chord formula is 1-3-5-b7 (i.e. the Root, 3rd, 5thand b7thnotes).
Inversions:
An inversion is simply a way of identifying when the notes of a chord have been ‘inverted’ i.e. when the root (1st) note of the chord is not in the lowest (bass) position.
The C dom 7 chord consists of 4 notes, C, E, G, Bb (1st–3rd–5th–b7th).
When the lowest note of the chord is C (1st) then it is in the ‘root position‘.
When the note E (3rd) is in the lowest position then the chord is known as a ‘1st inversion‘.
When the note G (5th) is in the lowest position then the chord is known as a ‘2nd inversion‘.
When the note Bb (b7th) is in the lowest position then the chord is known as a ‘3rd inversion‘.
The inversion is determined only by the note in the lowest (bass) position, it does not matter what order the other notes are in.
You can use MusicWheels™ to discover all the other dominant 7 chords and their notes.