Mendeleev
Periodic table · chemistry · physics
Element story

Actinium

Atomic number 89 means that every Actinium nucleus contains 89 protons. That proton count is the element's identity: change it and you no longer have Actinium.

Start with the nucleus

Atomic number 89 means that every Actinium nucleus contains 89 protons. That proton count is the element's identity: change it and you no longer have Actinium.

Actinium (Ac) is chemical element 89. 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.

Actinium sits in period 7, group 3 and the D 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 89 means that every Actinium nucleus contains 89 protons. That proton count is the element's identity: change it and you no longer have Actinium.

Keep exploring

→ Actinium · Atomic structure · Periodic trends

89AcActinium
Actinium · Ac · Z = 89

Actinium (Ac) is chemical element 89. 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

Actinium (Ac) is chemical element 89. 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 and neutron sources.

What its position in the table tells us

Actinium sits in period 7, group 3 and the D block. That location is useful because neighbouring elements often share trends in valence electrons, oxidation states and bonding behaviour.