Mendeleev
Periodic table · chemistry · physics
Element story

Einsteinium

Atomic number 99 means that every Einsteinium nucleus contains 99 protons. That proton count is the element's identity: change it and you no longer have Einsteinium.

Start with the nucleus

Atomic number 99 means that every Einsteinium nucleus contains 99 protons. That proton count is the element's identity: change it and you no longer have Einsteinium.

Einsteinium (Es) is chemical element 99. 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 99 means that every Einsteinium nucleus contains 99 protons. That proton count is the element's identity: change it and you no longer have Einsteinium.

Keep exploring

→ Einsteinium · Atomic structure · Periodic trends

99EsEinsteinium
Einsteinium · Es · Z = 99

Einsteinium (Es) is chemical element 99. 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

Einsteinium (Es) is chemical element 99. 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

Einsteinium 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.