But, as the Rebbe points out, the notions already had precedents within earlier Jewish thought, such as the Midrash which the Rebbe cites. Maimonides' cosmogony is certainly taken from the ideas of the Greek philosophers which had become accepted within Jewish circles. We are supposed to be made of the element earth, but we are primarily water the the name ADaM, actually indicates via the letters themselves. It is the number, rather than the ascribing a fixed property that appears to be important, which is why we get so many variations. YKVK written as per the letters, yields 44=DaM, also divisible by four. Their total gematria is 496, divisible by 4 and furthermore is the 4th world, ordinarily speaking, MaLCHVT. This leaves 4 letters that cannot reduce to D-L. This is the same gematria for the ordinals of AV, SaG, MaH and BoN, the 4 worlds. There is also the little known fact that 18 of the 22 letters reduce to a very simple formula, which are DaLeT and LaMeD. 1+2+3+4=10 an important part of Kabbalistic literature. The number 4 is extremely significant, perhaps more so than the idea of what the 4 can stand for. "Some hypothesize that they are four basic elements: positive, negative, antimatter, matter." In the cryptic note 1, the Rebbe says much as above, but adds a fascinating idea: I might also mention that there is another school that conceives these four Yesodot, not in their physical aspects but rather qualitatively, that is to say, "fire," in the sense of the properties of hot and dryness "water," in the sense of coolness and humidity, and so on. This does not mean something which under normal circumstances is indivisible or unchangeable, but the actual so-called "bricks" or components which make up everything that exists in the world. This should be borne in mind when we consider the term Yesodot in the Zohar, Midrash Rabba, Kabbalah, etc., and, of course, in the Tanya and other Chabad sources. Similarly, when we speak of an individual as being an element of society, this does not mean that the individual himself is not a composite. Even the term "atom" which originally meant something indivisible, is an archaism now employed only for convenience, as it no longer corresponds to its original meaning. For, as indicated above, a so-called element is not the most basic particle of matter.
Thus, the answer to your question already lies in the proper definition of the terms under discussion. But the atoms themselves are further made up of smaller particles, such as electrons, protons, neutrons, etc.
For the so-called elements are themselves made up of atoms, which are the smallest particles into which an element can be divided and yet retain its properties and characteristics. Two, modern chemistry does not recognize over one hundred basic elements, but a considerably fewer number if matter is to be reduced to its basic components or particles. One, the origin of that statement in the Tanya is not as you write, but it is to be found in Midrash Rabba, Bamidbar 14,12, טבעים, and at greater length and in greater detail in many parts of the Zohar, and further explained in other books of Kabbalah. Prefatorily, I must make at least two corrections in your letter. …you ask my explanation of the reference to the four "basic elements" ( yesodot) mentioned in chapter one of the Tanya, and you ask me how is it possible to reconcile this with modern chemistry which recognizes over one hundred elements. First, the letter, Dated 18th of Tevet, 5720 (January 16, 1960): I've seen two written responses on this topic from the Rebbe, one a letter written originally in English, the other, a cryptic note in Hebrew. I recognize this idea from ancient Greek and medieval philosophy, but it seems there's been some progress since then: my periodic table has 117 elements. The rabbi was talking about the "four elements"-earth, water, air and fire-as they are found in the human soul. I recently attended a class in Kabbalah and Chassidic Thought.