Elements cease to exist naturally when the number of protons in the nucleus exceeds a certain limit. This limit is known as the proton number or atomic number of the element beyond which it is not stable and cannot be found in nature. This limit is believed to be around atomic number 118, corresponding to the element Oganesson (Og).
Elements with atomic numbers higher than 118 have been synthesized in laboratories through nuclear reactions, but they are highly unstable and decay quickly. These superheavy elements are often referred to as transuranium or transactinide elements.
It is important to note that the exact limit beyond which elements cease to exist naturally is not yet precisely determined, and ongoing scientific research is aimed at exploring the properties and stability of superheavy elements.