Neptunium (Np)

Neptunium properties

Atomic number

93

Atomic mass

237 u

Category

Actinide

Group

—

Period

7

Block

f-block

State at room temp.

Solid

Electronegativity

1.36

Melting point

912 K (638.8 °C)

Boiling point

4,447 K (4,173.8 °C)

Density

20.45 g/cm³

Valence electrons

2

Common charges

+3, +4, +5, +6

Oxidation states

+6, +5, +4, +3

Atomic radius

221 pm

Ionization energy

6.266 eV

Electron affinity

—

Radioactive

Yes, no stable isotopes

Discovered

1940

Neptunium electron configuration

The electron configuration of Neptunium (Np) is [Rn] 5f4 6d1 7s2. Its 93 electrons are arranged in shells as 2, 8, 18, 32, 22, 9, 2.

Protons, neutrons and electrons in Neptunium

A neutral Neptunium atom has 93 protons and 93 electrons. Most Neptunium atoms have about 144 neutrons: the atomic mass rounded to 237, minus the atomic number 93.

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

How many valence electrons does Neptunium have?

2

Neptunium 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

Neptunium 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 Neptunium

237 g/mol

One mole of Neptunium atoms (6.022 × 10²³ atoms) has a mass of 237 grams. Use this value to convert between grams and moles.

Neptunium facts

• Neptunium was the first transuranium element, meaning the first element heavier than uranium ever made.
• Tiny traces of neptunium occur naturally in uranium ores, formed when uranium atoms capture neutrons.
• Neptunium (Np) has atomic number 93 and is a solid at room temperature. It was discovered in 1940.

Position in the periodic table

Neptunium is element 93, 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 Neptunium

Neptunium has no everyday uses. Neptunium-237, a by-product of nuclear reactors, is irradiated with neutrons to produce plutonium-238, which powers spacecraft such as the Voyager probes and NASA's Mars rovers Curiosity and Perseverance. Scientists also study neptunium because it is a long-lived part of spent nuclear fuel that must be stored safely.

Who discovered Neptunium?

Edwin McMillan and Philip Abelson made neptunium in 1940 at the University of California, Berkeley, by bombarding uranium with neutrons. It was named after the planet Neptune, the next planet beyond Uranus.

Where does the name come from?

Neptunium is named after the planet Neptune. Discovered in 1940, it was the first element beyond uranium, so it was named after the next planet out from Uranus, which honors the Roman god of the sea.

Discovery timeline