Why is G the seventh letter of the alphabet?

I was just wondering about that myself. My grandson is just learning the Alphabet song, and I think it’s nonsense. I learned by the whole word method, and letters just fall into words without being in any kind of alphabetical order.

It apparently started with the Greeks, Alpha, Beta, Gamma, and such.

G is actually the 3rd letter of the Greek alphabet. (well its equivalent)
It is unknown whether the earliest alphabets had a defined sequence

No idea why the English alphabet changed it to the seventh, I know the English alphabet has 2 more letters than the Greek.
Loads of history involved in the correct answer, its a great question. http://en.wikipedia.org/wiki/Alphabet

I get the impression that the order was not entirely intentional, but that order evolved over time. There’s a couple answers on this thread that provide some interesting history if you want to check it out.

Some ancient lettering systems were made up of symbols that had individual symbolic meaning of their own. Sometimes they were arranged a certain way to tell a story, such as the Futhark runes in northern Europe that symbolically represent the myth cycles there.

Other lettering systems also used some of the symbols to represent numerical values, such as in Rome or ancient Judea.

My guess is that at least some of ordering of the alphabet comes from some ancient arrangement like that.

Devanagari, the Alphabet used for Sanskrit and Hindi, is arranged in the order in which the human body can make sounds from the lowest parts of the vocalizing system up the throat into the mouth and to the lips in that order, with multiple letters in places where aspiration or longer expression makes them distinct.
I’m no linguist but that’s the only alphabet I know with clear, specific reasons for the order of all the letters. From what I can tell Arabic and Hebrew have some similarities but are not as consistent or complete.