Mendeleev
Periodic table · chemistry · physics
Element story

Protactinium

Atomic number 91 means that every Protactinium nucleus contains 91 protons. That proton count is the element's identity: change it and you no longer have Protactinium.

Start with the nucleus

Atomic number 91 means that every Protactinium nucleus contains 91 protons. That proton count is the element's identity: change it and you no longer have Protactinium.

Protactinium (Pa) is chemical element 91. 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 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 91 means that every Protactinium nucleus contains 91 protons. That proton count is the element's identity: change it and you no longer have Protactinium.

Keep exploring

→ Protactinium · Atomic structure · Periodic trends

91PaProtactinium
Protactinium · Pa · Z = 91

Protactinium (Pa) is chemical element 91. 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

Protactinium (Pa) is chemical element 91. 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 scientific research.

What its position in the table tells us

Protactinium 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.