Thulium
Atomic number 69 means that every Thulium nucleus contains 69 protons. That proton count is the element's identity: change it and you no longer have Thulium.
Start with the nucleus
Atomic number 69 means that every Thulium nucleus contains 69 protons. That proton count is the element's identity: change it and you no longer have Thulium.
Thulium (Tm) is chemical element 69. It belongs to the lanthanoids, and its reference state at room temperature is a solid. Those basic facts are a useful starting point for its chemistry and applications.
Thulium sits in period 6 and the F block. That location is useful because neighbouring elements often share trends in valence electrons, oxidation states and bonding behaviour.
See the atom
Conceptual visual: electron shells are a learning aid, not a literal picture of quantum orbitals.
What this number means
Atomic number 69 means that every Thulium nucleus contains 69 protons. That proton count is the element's identity: change it and you no longer have Thulium.