93NpNeptunium237[Rn] 5f⁴ 6d¹ 7s²
actinide

Neptunium

Neptunium is a chemical element with symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. Its position in the periodic table just after uranium, named after the planet Uranus, led to it being named after Neptune, the next planet beyond Uranus.

Properties

At a glance

Atomic number
93
Atomic mass
237 u
Phase
Solid
Density
20.45 g/cm³
Melting point
912 K
Boiling point
4,447 K
First ionization energy
604.5 kJ/mol
Electronegativity
1.36
Electron affinity
45.85 kJ/mol
Molar heat capacity
29.46 J/(mol·K)
Period
7
Appearance
silvery metallic

Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.

Electronic structure

Neptunium’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.

Electrons by shell
Electron configuration

86 is the [Rn] core total across six shells.

Preparing the orbital view…

93 protons144 neutrons

Neptunium-237: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.

States of matter

Turn up the heat

298 KK stands for kelvin, the temperature scale used in science. It starts at absolute zero (0 K), the coldest temperature possible, so it has no negative numbers and no degree sign.

A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid

At this temperature, neptunium is a solid.

At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.

Ionization energy

Pull the electrons off

Np

NpNeutral atom · no charge

A neutral neptunium atom. Removing its first electron takes 605 kJ/mol.

Neptunium’s outer shell holds 2 electrons. Electron 3 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 1.7× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.

Shell 1Shell 2Shell 3Shell 4Shell 5Shell 6Shell 7MeasuredEstimated or calculatedEnergy in kJ/molkJ/mol (kilojoules per mole) is the energy to remove that electron from every atom in a mole of them: about 602 sextillion (6.02 × 10²³) atoms. For a single atom, divide by 96.485 to get electronvolts (eV). Neptunium’s first electron takes about 6.3 eV.
1001,00010,000100,0001,000,00010,000,000100,000,000Shell 5Shell 4Shell 3×1.7×1.2×1.1×1.6×2.1×3.9151015202530354045505560657075808590
Show the values as a table
ElectronShellEnergy (kJ/mol)× previousValue
17605–Measured
271,1101.8Estimated
361,9011.7Estimated
463,2611.7Estimated
564,6311.4Calculated
666,2721.4Calculated
768,8771.4Calculated
8610,3241.2Calculated
9611,6751.1Calculated
10613,1221.1Calculated
11614,5691.1Calculated
12517,2711.2Calculated
13518,9111.1Calculated
14522,4811.2Calculated
15524,3141.1Calculated
16534,2521.4Calculated
17536,8571.1Calculated
18539,3661.1Calculated
19542,2611.1Calculated
20544,9621.1Calculated
21547,7601.1Calculated
22551,6201.1Calculated
23554,5141.1Calculated
24557,5051.1Calculated
25560,4001.1Calculated
26574,2941.2Calculated
27578,1531.1Calculated
28582,0131Calculated
29584,9071Calculated
30594,5561.1Calculated
31598,4151Calculated
325109,0281.1Calculated
335112,8881Calculated
344123,5011.1Calculated
354131,2201.1Calculated
364137,9741.1Calculated
374145,6931.1Calculated
384153,4121.1Calculated
394161,1311.1Calculated
404167,8841Calculated
414175,6031Calculated
424184,2871Calculated
434192,0061Calculated
444199,7251Calculated
454206,4791Calculated
464215,1621Calculated
474222,8811Calculated
484258,0981.2Calculated
494264,8521Calculated
504271,7991Calculated
514279,2291Calculated
524286,4651Calculated
534293,4121Calculated
544306,9201Calculated
554314,0601Calculated
564322,0681Calculated
574329,3041Calculated
584358,7321.1Calculated
594365,8721Calculated
604373,5911Calculated
614380,8281Calculated
624420,0011.1Calculated
634428,4911Calculated
644449,4291Calculated
654457,7261Calculated
663734,2531.6Calculated
673749,6911Calculated
683767,0581Calculated
693784,4261Calculated
703801,7931Calculated
713818,1961Calculated
723857,7551Calculated
733875,1221Calculated
743894,4191Calculated
753911,7861Calculated
763961,9591.1Calculated
773977,3961Calculated
783993,7991Calculated
7931,010,2011Calculated
8031,131,7731.1Calculated
8131,151,0701Calculated
8231,188,6991Calculated
8331,206,0671Calculated
8422,496,0762.1Calculated
8522,537,5641Calculated
8622,582,9121Calculated
8722,625,3661Calculated
8823,078,8471.2Calculated
8923,135,7731Calculated
9023,212,9621Calculated
9123,253,6981Calculated
92112,823,9623.9Calculated
93113,045,0101Calculated

Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.

Compared with other elements

How does it compare?

NeptuniumOther actinidesOther elements

Density

20.5 g/cm³5th highest of 99

Np

Melting point

912 K35th lowest of 96

Np

Boiling point

4,447 K11th highest of 97

Np

Electronegativity

1.3638th lowest of 96

Np

First ionization energy

605 kJ/mol38th lowest of 99

Np

Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.

Keep exploring

Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.