Einsteinium (Es)

Einsteinium properties

Atomic number

99

Atomic mass

252 u

Category

Actinide

Group

—

Period

7

Block

f-block

State at room temp.

Solid

Electronegativity

1.3

Melting point

1,133 K (859.8 °C)

Boiling point

1,269 K (995.8 °C)

Density

8.84 g/cm³

Valence electrons

2

Common charges

+3

Oxidation states

+3

Atomic radius

245 pm

Ionization energy

6.42 eV

Electron affinity

—

Radioactive

Yes, no stable isotopes

Discovered

1952

Einsteinium electron configuration

The electron configuration of Einsteinium (Es) is [Rn] 5f11 7s2. Its 99 electrons are arranged in shells as 2, 8, 18, 32, 29, 8, 2.

Protons, neutrons and electrons in Einsteinium

A neutral Einsteinium atom has 99 protons and 99 electrons. Most Einsteinium atoms have about 153 neutrons: the atomic mass rounded to 252, minus the atomic number 99.

Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass

How many valence electrons does Einsteinium have?

2

Einsteinium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.

See every element: Periodic table with valence electrons

Einsteinium orbital diagram

Each box is an orbital that holds up to two electrons with opposite spins (↑↓). The inner shells are the same as the noble gas in brackets. How to write electron configurations

Molar mass of Einsteinium

252 g/mol

One mole of Einsteinium atoms (6.022 × 10²³ atoms) has a mass of 252 grams. Use this value to convert between grams and moles.

Einsteinium facts

• The discovery of einsteinium was kept secret until 1955 because it came from a nuclear weapons test.
• Einsteinium is the element with the highest atomic number that has been seen in visible amounts in pure form.
• Einsteinium (Es) has atomic number 99 and is a solid at room temperature. It was discovered in 1952.

Position in the periodic table

Einsteinium is element 99, in period 7 of the periodic table. It is one of the Actinides in the f-block, shown in the rows below the main table.

All actinides

Uses of Einsteinium

Einsteinium has no uses outside basic research, because it is made only in tiny amounts and its isotopes decay quickly. Scientists use it to study the chemistry of the heaviest actinides, and in 1955 einsteinium-253 was the target that was bombarded with alpha particles to make the first atoms of mendelevium.

Who discovered Einsteinium?

A team led by Albert Ghiorso at Berkeley, working with Argonne and Los Alamos scientists, identified einsteinium in 1952 in the debris of 'Ivy Mike', the first full-scale hydrogen bomb test, in the Pacific. It was named after Albert Einstein.

Where does the name come from?

Einsteinium honors Albert Einstein, the physicist famous for the theory of relativity. The element was first found in 1952 in the debris of the first hydrogen bomb test, and its discovery and name were made public only in 1955, the year Einstein died.

Discovery timeline