In the Guitar Chords section of The Basics you can see that although major and minor guitar chords only contain notes from the triad, they look and sound quite different because it’s possible to play more than three notes at a time on the guitar.

Here are the chords in the key of C major as they would be played on the guitar:

Here are the chords for some other major keys:

Key of G

I G, II Am, III Bm, IV C, V D, VI Em, VII F#dim

Key of D

I D, II Em, III F#m, IV G, V A, VI Bm, VII C#dim

Key of A

I A, II Bm, III C#m, IV D, V E, VI F#m, VII G#dim

Key of E

I E, II F#m, III G#m, IV A, V B, VI C#m, VII D#dim

Key of F

I F, II Gm, III Am, IV Bb, V C, VI Dm, VII Edim