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No

Nobelium

Nobelium (No) is an actinide with atomic number 102. It has no stable isotope and no characteristic isotopic composition on Earth, so it has no standard atomic weight; its longest-lived isotope has mass number 259. Its electron configuration is [Rn] 5f14 7s2.

Nobelium key data

Symbol No
Atomic number 102
Mass number (longest-lived isotope) 259
Protons 102
Neutrons (longest-lived isotope, nobelium-259) 157
Electrons (neutral atom) 102
Category Actinide
Period 7
Group f-block, no group
Block f-block
Noble gas notation [Rn] 5f14 7s2
Full electron configuration 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

Mass number: IUPAC CIAAW radioactive elements, from NUBASE2020.

The values are facts and free to use; this page’s selection and presentation are © 2026 ScienceQuest.

Properties of nobelium

From PubChem, the US National Institutes of Health. Public domain. PubChem’s periodic table gives no value for the rows not shown. The discovery year is the year nobelium was first conclusively identified, from Wikipedia’s timeline of chemical element discoveries, in place of PubChem’s 1957.

Predicted melting point 1100 K (826.85 °C), joint 56th of 103 by melting point
Predicted state at room temperature Solid
Predicted electronegativity 1.3 (Pauling), joint 61st of 95 by electronegativity
First ionisation energy 6.65 eV (642 kJ/mol), 57th of 102 by first ionisation energy
Common oxidation states +3, +2
Discovered 1965

Each rank counts down from the highest value, among the elements PubChem’s table gives one for, and links to that property ranked across the whole table. All of them are collected under periodic trends.

Nobelium electron configuration

The full electron configuration of nobelium is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 5f14 6s2 6p6 7s2. With the noble-gas core collapsed it is [Rn] 5f14 7s2, and the outermost subshell is 7s2.

Bohr model of nobelium (No): a nucleus and seven shells holding 2, 8, 18, 32, 32, 8 and 2 electrons from the inside out.
Bohr model of nobelium (No). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.
Orbital box diagram of nobelium (No), [Rn] 5f14 7s2, with the radon core drawn as one bar: one box per orbital, filled by Hund’s rule, showing every orbital drawn holds a pair of electrons.
Orbital diagram of nobelium (No). Image © ScienceQuest, CC BY 4.0: free to reuse with credit to ScienceQuest and a link to this page, as the image licence explains.

Why group and block follow from this is set out in how the periodic table maps electron configuration, and the electron configuration of every element is listed on one page.

Mass of one nobelium atom

A molar mass is grams per mole, so dividing by the Avogadro constant gives the mass of a single atom, or for an element with more than one natural isotope the average mass of its atoms, and the reciprocal gives how many atoms sit in a gram.

Mass of one atom

  1. one atom = 259 / (6.02214076 × 10²³)
  2. = 4.3008 × 10⁻²² g

Atoms in one gram

  1. atoms per gram = 6.02214076 × 10²³ / 259
  2. = 2.3252 × 10²¹ atoms

Nobelium has no standard atomic weight, because it has neither a stable isotope nor a characteristic isotopic composition on Earth. The figure used above is the mass number of nobelium-259, so treat these as nominal.

Nobelium on the periodic table

Nobelium is in period 7, outside the numbered groups, in the f-block.

The rest of period 7

Work with nobelium