it's all music theory. do you know that chords are made up of scales? i can only explain to you from 5 to 7.. 9 + not too sure..
ok, from our do-re-mi, we know C major scale starts with C, then D, then E, F, G, A, B and back to see. then, there's intervals. it's basically the number of semitones between notes and scales. relating back to the C major scale: the intervals are...
C: 1st
D: Major 2nd
E: Major 3rd
F: Perfect 4th
G: Perfect 5th
A: Major 6th
B: Major 7th
C: Octave
look at your C Major chord it's made of intervals: 1st, 3rd, 5th (C, E, G)
if ya expand to a C Major 7 chord, it's made up of intervals as well: 1st, 3rd, 5th, 7th (C, E, G, B)
the C power chord is made up of only 2. can be 3 if ya add one octave: 1st, 5th (C, G) or 1st, 5th, octave (C, G, C)
oh well... hoped that answered half the question u asked...