Mendeleev
Periodic table · chemistry · physics
Element story

Thorium

Atomic number 90 means that every Thorium nucleus contains 90 protons. That proton count is the element's identity: change it and you no longer have Thorium.

Start with the nucleus

Atomic number 90 means that every Thorium nucleus contains 90 protons. That proton count is the element's identity: change it and you no longer have Thorium.

Thorium (Th) is chemical element 90. It belongs to the actinoids, 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 nuclear energy, alloys and scientific research.

See the atom

Conceptual visual: electron shells are a learning aid, not a literal picture of quantum orbitals.

What this number means

Atomic number 90 means that every Thorium nucleus contains 90 protons. That proton count is the element's identity: change it and you no longer have Thorium.

Keep exploring

→ Thorium · Atomic structure · Periodic trends

90ThThorium
Thorium · Th · Z = 90

Thorium (Th) is chemical element 90. It belongs to the actinoids, 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

Thorium (Th) is chemical element 90. It belongs to the actinoids, 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 nuclear energy, alloys and scientific research.

What its position in the table tells us

Thorium sits in period 7 and the F block. That location is useful because neighbouring elements often share trends in valence electrons, oxidation states and bonding behaviour.