Fermium
Fermium is a synthetic element with symbol Fm and atomic number 100. It is a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared.
At a glance
- Atomic number
- 100
- Atomic mass
- 257 u
- Phase
- Solid
- Density
- Unavailable
- Melting point
- 1,800 K
- Boiling point
- Unavailable
- First ionization energy
- 627.2 kJ/mol (estimated)
- Electronegativity
- 1.3
- Electron affinity
- 33.96 kJ/mol
- Molar heat capacity
- Unavailable
- Period
- 7
- Appearance
- Unavailable
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Fermium’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…
100 protons157 neutrons
Fermium-257: 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.
Pull the electrons off
FmNeutral atom · no charge
A neutral fermium atom. Removing its first electron takes 627 kJ/mol.
Fermium’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 1.9× 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 | 627 | – | Estimated |
| 2 | 7 | 1,196 | 1.9 | Estimated |
| 3 | 6 | 2,239 | 1.9 | Estimated |
| 4 | 6 | 3,792 | 1.7 | Estimated |
| 5 | 6 | 5,307 | 1.4 | Calculated |
| 6 | 6 | 7,140 | 1.3 | Calculated |
| 7 | 6 | 8,973 | 1.3 | Calculated |
| 8 | 6 | 11,578 | 1.3 | Calculated |
| 9 | 6 | 13,122 | 1.1 | Calculated |
| 10 | 6 | 15,631 | 1.2 | Calculated |
| 11 | 5 | 17,850 | 1.1 | Calculated |
| 12 | 5 | 20,165 | 1.1 | Calculated |
| 13 | 5 | 22,867 | 1.1 | Calculated |
| 14 | 5 | 24,797 | 1.1 | Calculated |
| 15 | 5 | 26,630 | 1.1 | Calculated |
| 16 | 5 | 28,946 | 1.1 | Calculated |
| 17 | 5 | 31,454 | 1.1 | Calculated |
| 18 | 5 | 33,866 | 1.1 | Calculated |
| 19 | 5 | 36,375 | 1.1 | Calculated |
| 20 | 5 | 38,787 | 1.1 | Calculated |
| 21 | 5 | 41,489 | 1.1 | Calculated |
| 22 | 5 | 43,708 | 1.1 | Calculated |
| 23 | 5 | 59,435 | 1.4 | Calculated |
| 24 | 5 | 62,426 | 1.1 | Calculated |
| 25 | 5 | 65,610 | 1.1 | Calculated |
| 26 | 5 | 69,083 | 1.1 | Calculated |
| 27 | 5 | 72,268 | 1 | Calculated |
| 28 | 5 | 75,452 | 1 | Calculated |
| 29 | 5 | 80,758 | 1.1 | Calculated |
| 30 | 5 | 84,039 | 1 | Calculated |
| 31 | 5 | 87,705 | 1 | Calculated |
| 32 | 5 | 91,082 | 1 | Calculated |
| 33 | 5 | 107,099 | 1.2 | Calculated |
| 34 | 5 | 110,958 | 1 | Calculated |
| 35 | 5 | 114,818 | 1 | Calculated |
| 36 | 5 | 118,677 | 1 | Calculated |
| 37 | 5 | 132,185 | 1.1 | Calculated |
| 38 | 5 | 137,009 | 1 | Calculated |
| 39 | 5 | 149,552 | 1.1 | Calculated |
| 40 | 5 | 154,377 | 1 | Calculated |
| 41 | 4 | 170,779 | 1.1 | Calculated |
| 42 | 4 | 178,498 | 1 | Calculated |
| 43 | 4 | 187,182 | 1 | Calculated |
| 44 | 4 | 195,865 | 1 | Calculated |
| 45 | 4 | 204,549 | 1 | Calculated |
| 46 | 4 | 213,233 | 1 | Calculated |
| 47 | 4 | 221,916 | 1 | Calculated |
| 48 | 4 | 230,600 | 1 | Calculated |
| 49 | 4 | 240,248 | 1 | Calculated |
| 50 | 4 | 249,897 | 1 | Calculated |
| 51 | 4 | 258,581 | 1 | Calculated |
| 52 | 4 | 266,300 | 1 | Calculated |
| 53 | 4 | 274,983 | 1 | Calculated |
| 54 | 4 | 284,632 | 1 | Calculated |
| 55 | 4 | 328,340 | 1.2 | Calculated |
| 56 | 4 | 335,769 | 1 | Calculated |
| 57 | 4 | 343,584 | 1 | Calculated |
| 58 | 4 | 351,882 | 1 | Calculated |
| 59 | 4 | 359,890 | 1 | Calculated |
| 60 | 4 | 367,609 | 1 | Calculated |
| 61 | 4 | 384,591 | 1 | Calculated |
| 62 | 4 | 392,695 | 1 | Calculated |
| 63 | 4 | 401,379 | 1 | Calculated |
| 64 | 4 | 409,580 | 1 | Calculated |
| 65 | 4 | 442,482 | 1.1 | Calculated |
| 66 | 4 | 450,587 | 1 | Calculated |
| 67 | 4 | 459,270 | 1 | Calculated |
| 68 | 4 | 466,989 | 1 | Calculated |
| 69 | 4 | 522,951 | 1.1 | Calculated |
| 70 | 4 | 531,634 | 1 | Calculated |
| 71 | 4 | 555,756 | 1 | Calculated |
| 72 | 4 | 565,404 | 1 | Calculated |
| 73 | 3 | 887,665 | 1.6 | Calculated |
| 74 | 3 | 904,068 | 1 | Calculated |
| 75 | 3 | 923,365 | 1 | Calculated |
| 76 | 3 | 942,662 | 1 | Calculated |
| 77 | 3 | 961,959 | 1 | Calculated |
| 78 | 3 | 980,291 | 1 | Calculated |
| 79 | 3 | 1,028,534 | 1 | Calculated |
| 80 | 3 | 1,047,831 | 1 | Calculated |
| 81 | 3 | 1,069,057 | 1 | Calculated |
| 82 | 3 | 1,088,355 | 1 | Calculated |
| 83 | 3 | 1,143,351 | 1.1 | Calculated |
| 84 | 3 | 1,159,754 | 1 | Calculated |
| 85 | 3 | 1,179,051 | 1 | Calculated |
| 86 | 3 | 1,195,453 | 1 | Calculated |
| 87 | 3 | 1,368,162 | 1.1 | Calculated |
| 88 | 3 | 1,389,389 | 1 | Calculated |
| 89 | 3 | 1,427,983 | 1 | Calculated |
| 90 | 3 | 1,447,280 | 1 | Calculated |
| 91 | 2 | 2,923,506 | 2 | Calculated |
| 92 | 2 | 2,971,748 | 1 | Calculated |
| 93 | 2 | 3,019,991 | 1 | Calculated |
| 94 | 2 | 3,068,234 | 1 | Calculated |
| 95 | 2 | 3,705,037 | 1.2 | Calculated |
| 96 | 2 | 3,772,576 | 1 | Calculated |
| 97 | 2 | 3,859,413 | 1 | Calculated |
| 98 | 2 | 3,905,939 | 1 | Calculated |
| 99 | 1 | 15,261,181 | 3.9 | Calculated |
| 100 | 1 | 15,515,613 | 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.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- FermiumRoyal Society of Chemistry
- FermiumWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database