Nobelium (No)

Nobelium is the only actinide whose most stable oxidation state is +2 rather than +3, because its 5f subshell is full and prying an electron out of it costs more than the chemistry gains — a relativistic effect that makes nobelium behave a little like the alkaline earth metals. It also has the messiest discovery history in the table: a Stockholm claim in 1957 could not be reproduced, Berkeley and Dubna both claimed it afterwards, and IUPAC eventually awarded priority to Dubna while keeping the Swedish name.

Properties

Atomic number

102

Symbol

No

Mass number of most stable isotope

[259]

Category

Actinide

Period

7

Block

f-block

Electron configuration

[Rn] 7s² 5f¹⁴

Electrons per shell

2, 8, 18, 32, 32, 8, 2

Oxidation states

+2, +3

Discovered

1966 by Georgy Flerov and colleagues at Dubna; earlier claims from Stockholm and Berkeley were not confirmed

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴

Noble gas shorthand

[Rn] 7s² 5f¹⁴

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 32 · P: 8 · Q: 2

What it is used for

• Research only; no application outside the laboratory

Hazards

• Intensely radioactive; exists only as individual atoms in an accelerator

Melting point, boiling point, density and electronegativity are omitted: no measured values exist. The mass given is the mass number of nobelium-259, the longest-lived at 58 minutes.

Several physical properties are not listed for nobelium because no bulk sample has ever existed. Only a handful of atoms have been produced, often with half-lives measured in seconds, so published melting points and densities for elements in this range are calculations rather than measurements. They are omitted rather than presented as observed values.

Neighbours in the table