Yes a basic chord is made up of 3 notes(remember a basic chord, there are other chords that are different, such as 7th chords). Instead of looking at it like ABC try to look at it like ACE.
Or if it helps in numbers. There are 7 notes in a scale.In a major key the major chords of that scale are 1,4 and 5. The minor being 2,3,6. Diminished being 7.A basic chord is made up of the root, the 3rd and the 5th.
For example, say we are playing in the Major key of C(no sharps and no flats).
A 1 chord would be made up of the notes CEG. A 2 chord would be made up of DFA. Follow that pattern to make a index of chords for a given key.
If we were playing in the Major key of D a index of chords would look like the following:
1(Major)-D F# A
2(Minor)-E G B
3(Minor)-F# A C#
4(Major)-G B D
5(Major)-A C# E
6(minor)-B D F#
7(Dim.)-C# E G
Hope that helps