Mendeleev
Periodic table · chemistry · physics
Element story

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.

Keep exploring

→ Thulium · Atomic structure · Periodic trends

69TmThulium
Thulium · Tm · Z = 69

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.

Understanding the element

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.

Where do we encounter it?

In practice, it turns up most often in lasers, xray sources and scientific research.

What its position in the table tells us

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.