Promethium (Pm)
Promethium is element 61, a lanthanide in the lanthanide series (period 6). A neutral atom has 61 protons, 84 neutrons and 61 electrons, 2 of them valence electrons.
Lanthanide- Atomic number
- 61
- Atomic mass
- 144.91 u
- Valence electrons
- 2*
- Protons · neutrons
- 61 · 84
- Electrons per shell
- 2, 8, 18, 23, 8, 2
- At room temperature
- solid
Bohr model of promethium
The Bohr model draws promethium as a nucleus of 61 protons and 84 neutrons, with its 61 electrons on 6 circular shells: 2 in shell 1, 8 in shell 2, 18 in shell 3, 23 in shell 4, 8 in shell 5, 2 in shell 6. Press Build the atom to watch the shells fill from the inside out. The outer ring (the P shell) is dashed: the electrons there are the ones that take part in chemistry.
Real electrons don't travel in neat circles. They live in fuzzy orbitals, shown below, but the Bohr picture is the quickest way to count shells and valence electrons.
Electron configuration of promethium
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁵
Short form (noble gas notation): [Xe] 6s² 4f⁵. The [Xe] stands for the electrons of xenon, the noble gas before it.
How many valence electrons does promethium have?
Promethium has 2 valence electrons.
Promethium is a lanthanide, so its valence electrons are less clear-cut than for main-group elements. It has 2 electrons in its outermost shell (shell 6), and electrons in its inner f and d subshell can also take part in bonding.
Protons, neutrons and electrons
| Protons | 61 | equal to the atomic number |
|---|---|---|
| Electrons | 61 | equal to the protons in a neutral atom |
| Neutrons | 84 | mass number 145 − 61 protons |
Atoms of the same element can have different numbers of neutrons (isotopes). The count above uses the rounded atomic mass, the way it's taught in class.
Promethium properties
| Symbol | Pm |
|---|---|
| Category | Lanthanide |
| Group · period · block | — · 6 · f |
| Atomic mass | 144.91 u |
| State at 25 °C | solid |
| Melting point | 1,315 K (1,040 °C, 1,910 °F) |
| Boiling point | 3,273 K (3,000 °C, 5,430 °F) |
| Density | 7.26 g/cm³ |
| Electronegativity (Pauling) | — |
| Atomic radius | 236 pm |
| First ionization energy | 5.55 eV |
| Electron affinity | — |
| Oxidation states | +3 |
| Common ion charge | +3 |
| Discovered | 1945 by Chien Shiung Wu |
Where promethium sits on the periodic table
Lanthanides: Lanthanum, Cerium, Praseodymium, Neodymium, Samarium, Europium, Gadolinium, Terbium.
Questions about promethium
How many valence electrons does promethium have?
Promethium has 2 valence electrons in its outer shell; inner d or f electrons can also bond.
How many protons, neutrons and electrons does promethium have?
A neutral promethium atom has 61 protons and 61 electrons. Its most common form has about 84 neutrons (mass number 145 − 61 protons).
What is the electron configuration of promethium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f⁵, written in short form as [Xe] 6s² 4f⁵.
What does the Bohr model of promethium look like?
A nucleus of 61 protons and 84 neutrons, circled by 6 electron shells holding 2, 8, 18, 23, 8, 2 electrons.
What is the atomic number of promethium?
61. The atomic number is the number of protons in the nucleus, and it is what makes an atom promethium.