Here's why:

* Atomic Number: The atomic number of an element defines its identity. It's the number of protons in the nucleus of an atom.

* Beryllium's Atomic Number: Beryllium has an atomic number of 4, meaning it has 4 protons in its nucleus.

So, any atom with 4 protons is a beryllium atom, regardless of the number of neutrons (which determine the isotope).