Nobelium (No)
Element 102 · Actinide · atomic mass [259] u · f-block, period 7
Electron shells: 2, 8, 18, 32, 32, 8, 2
Nobelium's discovery was disputed for years between Swedish, American and Soviet teams. Unusually for an actinide, its most stable ionic state is +2 rather than +3.
Three separate labs claimed nobelium; the name proposed by the team whose claim failed is the one that stuck.
- Atomic number
- 102
- Atomic mass
- [259] u
- Electron configuration
- [Rn] 7s² 5f¹⁴
- Group · period · block
- f-block · 7 · f
- Oxidation states
- +2, +3
- Electronegativity
- 1.3 (Pauling)
- Melting point
- 827 °C
- Boiling point
- —
- Density
- Not measured
- State at 20 °C
- Solid
- Appearance
- Unknown; presumed metallic
- Discovered
- Joint Institute for Nuclear Research, Dubna, 1957
102 protons, and 102 electrons when neutral
Mass number of the longest-lived isotope — no standard atomic weight exists
Shown in the strip below the table
What Nobelium is used for
- Scientific research only
Atomic structure of Nobelium
A neutral nobelium atom has 102 protons and 102 electrons. Its most common isotope carries about 157 neutrons, which is where the mass number 259 comes from. Change the neutron count and you have a different isotope of nobelium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 32, 8, 2. In orbital notation that is [Rn] 7s² 5f¹⁴. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Nobelium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Nobelium sits in the periodic table
The second f-block row, elements 89-103. All are radioactive, and everything past uranium is essentially man-made.
- One proton lighter: Mendelevium.
- One proton heavier: Lawrencium.
Discovery and naming
Nobelium was discovered by Joint Institute for Nuclear Research, Dubna in 1957. Its name comes from Alfred Nobel.
Every isotope of nobelium is radioactive, so it has no standard atomic weight. Periodic tables show the mass number of its longest-lived isotope in square brackets instead.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Nobelium?
Nobelium has no stable isotope, so it has no standard atomic weight. Periodic tables instead show 259 in square brackets — the mass number of its longest-lived isotope.
How many protons, neutrons and electrons does Nobelium have?
Nobelium has 102 protons, because the atomic number is the proton count and that is what makes an atom Nobelium at all. A neutral Nobelium atom has the same number of electrons, 102. The neutron count varies by isotope; the most common one has about 157, since 259 − 102 = 157.
What is the electron configuration of Nobelium?
The electron configuration of Nobelium is [Rn] 7s² 5f¹⁴. Its electrons are arranged 2, 8, 18, 32, 32, 8, 2 across 7 shells.
Is Nobelium a metal?
Yes. Nobelium is classified as a actinide, on the metallic side of the table.
What group and period is Nobelium in?
Nobelium sits in the f-block strip below the main table, in period 7, among the actinides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Nobelium?
Nobelium most commonly forms a 2+ or 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Nobelium?
Nobelium melts at 827 °C. That puts it in the solids at everyday temperatures.
What is Nobelium used for?
Scientific research only. Nobelium's discovery was disputed for years between Swedish, American and Soviet teams.
Who discovered Nobelium, and where does its name come from?
Nobelium (No) was discovered by Joint Institute for Nuclear Research, Dubna in 1957. The name comes from Alfred Nobel.
Is Nobelium radioactive?
Yes. Every isotope of Nobelium is radioactive — it has no stable form at all, which is why the periodic table shows its mass in square brackets rather than as a standard atomic weight.