Plutonium
Plutonium is a transuranic radioactive chemical element with symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation states.
At a glance
- Atomic number
- 94
- Atomic mass
- 244 u
- Phase
- Solid
- Density
- 19.816 g/cm³
- Melting point
- 912.5 K
- Boiling point
- 3,505 K
- First ionization energy
- 581.4 kJ/mol
- Electronegativity
- 1.28
- Electron affinity
- -48.33 kJ/mol
- Molar heat capacity
- 35.5 J/(mol·K)
- Period
- 7
- Appearance
- silvery white, tarnishing to dark gray in air
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Plutonium’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.
86 is the [Rn] core total across six shells.
Preparing the orbital view…
94 protons150 neutrons
Plutonium-244: 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.
Turn up the heat
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, plutonium 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.
Pull the electrons off
PuNeutral atom · no charge
A neutral plutonium atom. Removing its first electron takes 581 kJ/mol.
Plutonium’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 1.8× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.
What does this tell us?
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 7 | 581 | – | Measured |
| 2 | 7 | 1,110 | 1.9 | Estimated |
| 3 | 6 | 2,036 | 1.8 | Estimated |
| 4 | 6 | 3,377 | 1.7 | Estimated |
| 5 | 6 | 4,728 | 1.4 | Calculated |
| 6 | 6 | 7,719 | 1.6 | Calculated |
| 7 | 6 | 9,166 | 1.2 | Calculated |
| 8 | 6 | 10,517 | 1.1 | Calculated |
| 9 | 6 | 11,964 | 1.1 | Calculated |
| 10 | 6 | 13,411 | 1.1 | Calculated |
| 11 | 5 | 15,341 | 1.1 | Calculated |
| 12 | 5 | 17,271 | 1.1 | Calculated |
| 13 | 5 | 19,297 | 1.1 | Calculated |
| 14 | 5 | 21,130 | 1.1 | Calculated |
| 15 | 5 | 24,893 | 1.2 | Calculated |
| 16 | 5 | 26,823 | 1.1 | Calculated |
| 17 | 5 | 37,533 | 1.4 | Calculated |
| 18 | 5 | 40,138 | 1.1 | Calculated |
| 19 | 5 | 42,839 | 1.1 | Calculated |
| 20 | 5 | 45,734 | 1.1 | Calculated |
| 21 | 5 | 48,532 | 1.1 | Calculated |
| 22 | 5 | 51,330 | 1.1 | Calculated |
| 23 | 5 | 55,479 | 1.1 | Calculated |
| 24 | 5 | 58,374 | 1.1 | Calculated |
| 25 | 5 | 61,461 | 1.1 | Calculated |
| 26 | 5 | 64,452 | 1 | Calculated |
| 27 | 5 | 79,118 | 1.2 | Calculated |
| 28 | 5 | 82,013 | 1 | Calculated |
| 29 | 5 | 85,872 | 1 | Calculated |
| 30 | 5 | 89,731 | 1 | Calculated |
| 31 | 5 | 99,380 | 1.1 | Calculated |
| 32 | 5 | 103,239 | 1 | Calculated |
| 33 | 5 | 113,853 | 1.1 | Calculated |
| 34 | 5 | 117,712 | 1 | Calculated |
| 35 | 4 | 129,290 | 1.1 | Calculated |
| 36 | 4 | 137,009 | 1.1 | Calculated |
| 37 | 4 | 144,728 | 1.1 | Calculated |
| 38 | 4 | 152,447 | 1.1 | Calculated |
| 39 | 4 | 160,166 | 1.1 | Calculated |
| 40 | 4 | 167,884 | 1 | Calculated |
| 41 | 4 | 175,603 | 1 | Calculated |
| 42 | 4 | 182,357 | 1 | Calculated |
| 43 | 4 | 192,006 | 1.1 | Calculated |
| 44 | 4 | 199,725 | 1 | Calculated |
| 45 | 4 | 207,443 | 1 | Calculated |
| 46 | 4 | 215,162 | 1 | Calculated |
| 47 | 4 | 222,881 | 1 | Calculated |
| 48 | 4 | 230,600 | 1 | Calculated |
| 49 | 4 | 267,650 | 1.2 | Calculated |
| 50 | 4 | 274,404 | 1 | Calculated |
| 51 | 4 | 281,544 | 1 | Calculated |
| 52 | 4 | 289,167 | 1 | Calculated |
| 53 | 4 | 296,403 | 1 | Calculated |
| 54 | 4 | 303,543 | 1 | Calculated |
| 55 | 4 | 317,437 | 1 | Calculated |
| 56 | 4 | 324,770 | 1 | Calculated |
| 57 | 4 | 332,778 | 1 | Calculated |
| 58 | 4 | 340,304 | 1 | Calculated |
| 59 | 4 | 370,118 | 1.1 | Calculated |
| 60 | 4 | 377,354 | 1 | Calculated |
| 61 | 4 | 385,266 | 1 | Calculated |
| 62 | 4 | 392,502 | 1 | Calculated |
| 63 | 4 | 433,798 | 1.1 | Calculated |
| 64 | 4 | 442,385 | 1 | Calculated |
| 65 | 4 | 463,805 | 1 | Calculated |
| 66 | 4 | 471,813 | 1 | Calculated |
| 67 | 3 | 755,480 | 1.6 | Calculated |
| 68 | 3 | 770,918 | 1 | Calculated |
| 69 | 3 | 788,285 | 1 | Calculated |
| 70 | 3 | 806,617 | 1 | Calculated |
| 71 | 3 | 823,985 | 1 | Calculated |
| 72 | 3 | 840,387 | 1 | Calculated |
| 73 | 3 | 880,911 | 1 | Calculated |
| 74 | 3 | 898,278 | 1 | Calculated |
| 75 | 3 | 918,540 | 1 | Calculated |
| 76 | 3 | 935,908 | 1 | Calculated |
| 77 | 3 | 987,045 | 1.1 | Calculated |
| 78 | 3 | 1,002,483 | 1 | Calculated |
| 79 | 3 | 1,019,850 | 1 | Calculated |
| 80 | 3 | 1,035,288 | 1 | Calculated |
| 81 | 3 | 1,163,613 | 1.1 | Calculated |
| 82 | 3 | 1,182,910 | 1 | Calculated |
| 83 | 3 | 1,221,504 | 1 | Calculated |
| 84 | 3 | 1,238,872 | 1 | Calculated |
| 85 | 2 | 2,554,932 | 2.1 | Calculated |
| 86 | 2 | 2,597,385 | 1 | Calculated |
| 87 | 2 | 2,643,698 | 1 | Calculated |
| 88 | 2 | 2,686,152 | 1 | Calculated |
| 89 | 2 | 3,164,719 | 1.2 | Calculated |
| 90 | 2 | 3,222,610 | 1 | Calculated |
| 91 | 2 | 3,290,150 | 1 | Calculated |
| 92 | 2 | 3,340,882 | 1 | Calculated |
| 93 | 1 | 13,151,443 | 3.9 | Calculated |
| 94 | 1 | 13,376,746 | 1 | Calculated |
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.
Watching atoms decay
Plutonium-239 is made in nuclear reactors. When it decays it becomes uranium-235, which starts a chain of its own and ends as a different kind of lead.
Half of any sample of Pu-239 decays every 24,100 years, turning into U-235.
Half-lives passed (1 half-life = 24,100 years)
No time passed · 0 half-lives · 100 of 100 atoms left
Each atom decays at a random moment, so no one can say which will go next, but about half of whatever is left goes in every half-life. The dashed curve is the prediction; the solid line is this sample. The new U-235 atoms decay too, on their own schedule, which the chain below follows.
From Pu-239 to stable Pb-207: 12 steps
- Pu-239Plutonium24,000 yearsαdecays by alpha
- U-235Uranium700 million yearsαdecays by alpha
- Th-231Thorium1.1 daysβdecays by beta
- Pa-231Protactinium33,000 yearsαdecays by alpha
- Ac-227Actinium22 yearsβdecays by beta
- Th-227Thorium19 daysαdecays by alpha
- Ra-223Radium11 daysαdecays by alpha
- Rn-219Radon4 secondsαdecays by alpha
- Po-215Polonium1.8 millisecondsαdecays by alpha
- Pb-211Lead36 minutesβdecays by beta
- Bi-211Bismuth2.1 minutesαdecays by alpha
- Tl-207Thallium4.8 minutesβdecays by beta
- Pb-207Leadstable
Arrows show how each atom decays: α gives off an alpha particle (2 protons and 2 neutrons), β turns a neutron into a proton, γ gives off a gamma ray.
Half-lives and decay modes from the IAEA Live Chart of Nuclides (evaluated ENSDF data). The chain follows each atom’s most common decay; a few steps have rare side branches.
How does it compare?
Density
19.8 g/cm³6th highest of 99
Melting point
913 K36th lowest of 96
Boiling point
3,505 K25th highest of 97
Electronegativity
1.2830th lowest of 96
First ionization energy
581 kJ/mol28th lowest of 99
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.
- PlutoniumRoyal Society of Chemistry
- PlutoniumWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database