Astatine
Atomic number 85 means that every Astatine nucleus contains 85 protons. That proton count is the element's identity: change it and you no longer have Astatine.
Start with the nucleus
Atomic number 85 means that every Astatine nucleus contains 85 protons. That proton count is the element's identity: change it and you no longer have Astatine.
Astatine (At) is chemical element 85. It belongs to the halogens, and its reference state at room temperature is a solid. Those basic facts are a useful starting point for its chemistry and applications.
In practice, it turns up most often in scientific research, nuclear medicine and chemical synthesis.
See the atom
Conceptual visual: electron shells are a learning aid, not a literal picture of quantum orbitals.
What this number means
Atomic number 85 means that every Astatine nucleus contains 85 protons. That proton count is the element's identity: change it and you no longer have Astatine.