ActinideElement 102 · f-block

Nobelium (No)

Nobelium (No) is an actinide with atomic number 102; its most stable known isotope has mass number 259. At room temperature it is a solid that melts at 827 °C (estimated).

102NoNobelium[259]

Atomic number

102

protons

Atomic weight

[259]

most stable isotope

Melting point

827 °C

estimated

Boiling point

—

Density

9.9 g/cm³

predicted

Electronegativity

1.3

Pauling scale

State at 25 °C

Solid

Discovered

1966

USSR (Dubna)

Nobelium at a glance

Identity

Symbol	No
Atomic number (Z)	102
Atomic weight	[259] mass number of the most stable isotope
Category	Actinide
Group	— (f-block: actinide series)
Period	7
Block	f-block
CAS number	10028-14-5

Atomic properties

Electron configuration	[Rn] 5f¹⁴ 7s² Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 7s²
Electrons per shell	2, 8, 18, 32, 32, 8, 2
Oxidation states	+3 Less common: +2
Electronegativity (Pauling)	1.3
First ionisation energy	6.626 eV (639.3 kJ/mol) 2nd: 12.93 eV · 3rd: 25.8 eV
Covalent radius	176 pm
Van der Waals radius	246 pm

Physical properties

State at 25 °C	Solid
Melting point	827 °C · 1,520.6 °F · 1,100.15 K estimated
Density	9.9 g/cm³ (predicted)

Isotopes & abundance

Natural occurrence	Synthetic
Radioactive	Yes
Stable isotopes	1
Most stable isotope	²⁵⁹No — half-life 58 min
Known isotopes	17

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Nobelium electron configuration

Nobelium has 102 electrons. Written in short form, its ground-state configuration is [Rn] 5f¹⁴ 7s² — the electrons of the noble gas radon, plus 5f¹⁴ 7s².Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 7s².

5f↑↓↑↓↑↓↑↓↑↓↑↓↑↓

7s↑↓

Discovery and name

Discovered

1966 — Joint Institute for Nuclear Research (Georgy Flerov's group) · USSR (Dubna).

Name

Alfred Nobel.

Known for

Only made in particle accelerators; its discovery was disputed for years between laboratories in Sweden, the USA and the USSR.

Isotopes of nobelium

Nobelium has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
²⁵⁹No	102	157	58 min

17 isotopes of nobelium are known in our data set (half-lives as published in nuclear data tables).

Nobelium and its neighbours in the actinide series

Neighbouring elements in the same f-block series:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Einsteinium	99	[252]	860 °C (est.)	—	8.84 g/cm³ (pred.)	1.3
Fermium	100	[257]	1,527 °C (est.)	—	9.7 g/cm³ (pred.)	1.3
Mendelevium	101	[258]	827 °C (est.)	—	10.3 g/cm³ (pred.)	1.3
Nobelium	102	[259]	827 °C (est.)	—	9.9 g/cm³ (pred.)	1.3
Lawrencium	103	[266]	1,627 °C (est.)	—	15.6 g/cm³ (pred.)	1.3

Frequently asked questions

6 answers

What is the atomic mass of nobelium?

Nobelium has no stable isotopes, so it has no standard atomic weight. Periodic tables show [259], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does nobelium have?

A neutral nobelium atom has 102 protons and 102 electrons. Its most stable isotope, nobelium-259, has 157 neutrons.

What is the electron configuration of nobelium?

[Rn] 5f¹⁴ 7s² (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 7s²).

What are the melting and boiling points of nobelium?

Nobelium melts at 827 °C (1,520.6 °F) (estimated).

Is nobelium a metal?

Nobelium is a metal. It is in the f-block, period 7, and is a solid at room temperature.

Who discovered nobelium?

1966 — Joint Institute for Nuclear Research (Georgy Flerov's group) (USSR (Dubna)).