A chemical element, according to today's definition, consists exclusively of atoms with the same proton number (nuclear charge number = atomic number of the element) in the nucleus. Chemical elements are pure substances which, according to the original definition by Robert Boyle, in contrast to chemical compounds, cannot be further decomposed or converted into each other by chemical means.
From an anthroposophical-spiritual-scientific point of view, the matter is quite different. Behind the chemical elements are not hypothetically conceived atomic structures, but rather ahrimanic powers, which do not act at present, but from the past.
„Suppose some natural philosopher ponders, ponders what is behind the phenomena of nature. Well, he makes all kinds of theories and hypotheses about atomic connections and the like. But that is not the way it is. Behind what is spreading around us in a sensuous way is not really what natural philosophers usually assume, but behind all this is the sum of the Ahrimanic powers, but not as present. So if the natural philosopher is compelled, let us say, to suppose any atomic structures behind the chemical elements, that is wrong; behind the chemical elements are ahrimanic powers. But if you could lift what you see from the chemical elements and look behind them, you would see nothing behind them in the present: there it would be hollow, where you look for the atoms, and what works works into this hollow from the past. That is how it is in reality. Hence these many unsuccessful theories about that which is the "thing in itself"; for this "thing in itself" is not there at all in the present. Rather, at the place where the "thing in itself" is sought, there is nothing; but the effect is there from the past.“ (Lit.:GA 183, p. 168f)