There is no rule requiring that the root of the chord be the lowest note played…
In fact, you can create a wonderful variety of melodic and harmonic effects by using other chord tones as the lowest note.
Using a chord tone other that the root of the chord is known as Inversion.
Let’s see how inversion works to create harmonic tension and forward motion applied to a C Major Triad…
Root Position
A C chord (C-E-G) played with its root C as the lowest note, called the Root Position, sounds quite stable…
First Inversion
The C chord can also be played with the note E in the bass. This is called the First Inversion.
You might recognize this sounds from Eric Clapton’s “Layla”. In this case, the inversion is used to create harmonic instability and melodic interest in the bass line that naturally moves from the I to IV chord.
Second Inversion
A C chord can also be played with G in the bass. This is called the Second Inversion.
This as a very common way to prepare to end a piece, where C/G functions as a double suspended V chord that accentuates the dominant harmony before resolving to the tonic I.
