Where do chords get thier name from

Major chords are formed from the 1st, 3rd, and 5th notes of the major scale. Minor chords have a lowered third - just like the minor scale.

We don't form minor chords from minor scales, though, because there are several different minor scales. We just call them minor because of the lowered third... every minor scale also has a lowered third. It's what gives the scales/chords a minor sound.

In the key of C the the chords I belive are " C, Dm, Em, F, G, Am, " why are some of the Chords called major and some minor.

If you're asking why is it that some chords are major and some are minor in any given key, it's because of the unequal spacings or intervals between their notes. Those intervals are thirds (spanning 3 scale degrees) but are not all equally sized thirds - some are major thirds and some are minor thirds. Whether the chord will be called major or minor depends on how the thirds are arranged.

In the example you gave, the chords consist of the notes of the C major scale as follows:
C maj = C E G = Maj 3rd + min 3rd
C to E is a major third and E to G is a minor third.
Another way to look at it is by counting intervals only from the root of the chord:
C to E is a major third: C to G is a perfect fifth

D min = D F A = min 3rd + maj 3rd (or min 3 +P5)
E min = E G B = min 3rd + maj 3rd (or min 3 + P5)
F maj = F A C = maj 3rd + min 3rd (or maj 3 + P5)
G maj = G B D = maj 3rd + min 3rd (or maj 3 + P5)
A min = A C E = min 3rd + maj 3rd (or min 3 + P5)

Maj 3rd + min 3rd - (or maj 3 + P5) is called a major chord
min 3rd + maj 3rd - (or min 3 + P5) is called a minor chord

Another chord from the major scale that you didn't mention would, (in the key of C) be the notes B D F.
B to D is a min 3rd and D to F is also a minor third
or B to D is a min 3rd and B to F is a diminished fifth. This type of chord is called diminished.
One more possibility exists in arranging major and minor thirds. That is a chord consisting of two major thirds. They don't occur naturally among notes of the major scales but occur in modified minor scales.
For example, the notes C E G# make the chord C augmented.
C to E is a major third and E to G# is also a major third.
Or, C to E is a major third and C to G# is an augmented fifth. Such chords are called augmented

Thanks for the repies guys I think it has sunken into the grey matter.

I was searching my theory books but couldn't find the answer, I have printed out that explanation fretsource and will stick it into my books.

I got my pen and paper out and did some 1-3-5 intervals having all the notes written down in front of me helped.

So with Major and minor chords using the 1st 3rd and 5th there is an interval of 7 semi tones. If the first interval is 4 semitones and the second is 3 then you have a Major chord, and a minor chord if its the other way around.

thanks again