Atoms of one element will always be different from all the other elements because of their atomic number.
The atomic number is the number of protons in the nucleus of an atom. Each element has a unique atomic number, which determines the number of protons in the nucleus and, in turn, the number of electrons that orbit the nucleus. It defines the chemical properties and behavior of an element.
For example, Hydrogen has an atomic number of 1, and Helium has an atomic number of 2.
Because of this unique number of protons, the atoms of each element have unique properties and behave differently in chemical reactions.
It's worth noting that, isotopes of an element have the same atomic number, but different number of neutrons in the nucleus, this gives them the same chemical properties but different physical properties, like atomic mass.