it is my understanding that the number of elements is seven,
four we know and use and continue to master in different ways;
as we are ready to use them the others will begin to be more apparent,
not sure what the names have been called for the new powers

http://en.wikipedia.org/wiki/Metatron

http://www.marquette.edu/maqom/metatronsecrets.html

Metatron, is the one to whom God revealed “all the mysteries of wisdom, all the depths of the perfect Torah and all the thoughts of men’s hearts.”[1] The text leaves the impression that the fullness of the disclosure of the ultimate secrets to this angel can be comparable only to the knowledge of the Deity itself, since according to

Metatron, all the mysteries of the world and all the orders (secrets)[2] of creation are revealed before him “as they stand revealed before the Creator”[3] himself.

3 Enoch’s emphasis on understanding the mysteries of the human heart is also discernible in the early Enochic lore, namely, in 2 Enoch 50:1, when the seventh antediluvian patriarch reveals to his children that he is the one who is able to see the hidden deeds of each person as in a mirror: “I have set down the achievements of each person in the writings and no one can (hide himself) who is born on the earth, nor (can) his achievement be kept secret. I see everything, as if in a mirror.”

it is said that metatron could be thoth of egypt or hermes of the grec.

Consequently, Thoth gradually became seen as a god of wisdom, magic, and the measurement, and regulation, of events, and of time. He was thus said to be the secretary and counselor of Ra, and with Ma'at (truth/order) stood next to Ra on the nightly voyage across the sky, Ra being a sun god.

http://en.wikipedia.org/wiki/Thoth

In Greece itself the other gods have been depicted holding a caduceus, but it was mainly associated with Hermes. It was said to have the power to make people fall asleep or wake up, and also made peace between litigants, and is a visible sign of his authority, being used as a scepter. He was represented in doorways, possibly as an amulet of good fortune, or as a symbol of purification.

also roman mercury

Today, Mercury is regarded as the ruler of the third and sixth houses; traditionally, it ruled the 6th house, and had joy in the first house. Mercury is the messenger of the gods in mythology. It is the planet of day-to-day expression and relationships. Mercury's action is to take things apart and put them back together again. It is an opportunistic planet, decidedly unemotional and curious.

Mercury rules over Wednesday. In Romance languages, the word for Wednesday is often similar to Mercury (miercuri in Romanian, mercredi in French, miercoles in Spanish and "mercoledì" in Italian). Dante Alighieri associated Mercury with the liberal art of dialectic.[citation needed] In Chinese astrology, Mercury is ruled by the element water, which is diplomatic, kind, and intuitive. In Indian astrology, Mercury is called Budha, a word related to Buddhi ("intelligence"), and represents communication.[

http://en.wikipedia.org/wiki/Hermes

http://en.wikipedia.org/wiki/Mercury_(astrology)#Mercury

experience and enjoy.

Perhaps...perhaps..you are referring to the Caballa, of course, which is where your idea begins... but there are more than four archangels, and our friend Metatron is above them all... so, I see where you are coming from. However, I think that I prefer to leave Metatron as the Highest of Angels, the Scribe of God (as He has been called)- I believe that the angelic realm would have very little to do with Earthly elements...Their role as angels is as intercessors, messengers, and intermediaries between people and God. It seems almost sacrilegious to me to give this Highest of Angelic Creatures such a "physical" role on Earth...Just my Christian opinion.

Blessings to you, Jai

I think we shouldn't confuse Metatron with Hermes, nor Mercury.

The Sun sphere is ruled by a total of 45 genii. Their ruler, called "Master of the Sun Sphere" in the hermetic language, is named Mettatron in quabbalah. In the original quabbalistic scriptures Mettatron is called the mediator between God and man.

http://athenaeum.asiya.org/Bardon_Magical_Evocation.pdf page 299

As for the answer to the main question, the fifth element is akasa (or akasha).

1. Akasa or the Ethereal Principle ~ Several times while describing the elements I have said that they proceed from the ethereal principle. Accordingly, the ethereal principle is the ultimate, the supreme, the most powerful thing, something inconceivable, the ultimate cause of all things existing and created. To put it in a nutshell, it is the causal sphere. Therefore akasa is spaceless and timeless. It is the non-created, the incomprehensible, the indefinable. The various religions have given it the name of God. It is the fifth power, the original power. Everything has been created by it and is kept in balance by it. It is the origin and the purity of all thoughts and intentions, it is the causal world wherein the whole creation in subsisting on, beginning from the highest spheres down to the lowest ones. It is the quintessence of the alchemists; it is all in all.

http://www.infinite-beyond.com/scripts/bardon_initiation.pdf taken from the theory part.

As for the correspondences to the elements, I think that God himself corresponds to akasa.