Promethium (Pm)
Promethium is the only lanthanide with no stable isotopes, so almost none of it exists naturally on Earth.
Promethium properties
- Atomic mass
- 145 u
- Category
- Lanthanide
- Group
- —
- Period
- 6
- Block
- f-block
- State at room temp.
- Solid
- Melting point
- 1,315 K (1,041.8 °C)
- Boiling point
- 3,273 K (2,999.8 °C)
- Density
- 7.26 g/cm³
- Atomic radius
- 236 pm
- Ionization energy
- 5.55 eV
- Electron affinity
- —
- Radioactive
- Yes, no stable isotopes
- Discovered
- 1945
Promethium electron configuration
- Electron configuration
- [Xe] 4f5 6s2
- Full electron configuration
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f5 5s2 5p6 6s2
- Electron shells
- 2 · 8 · 18 · 23 · 8 · 2
The electron configuration of Promethium (Pm) is [Xe] 4f5 6s2. Its 61 electrons are arranged in shells as 2, 8, 18, 23, 8, 2.
Protons, neutrons and electrons in Promethium
A neutral Promethium atom has 61 protons and 61 electrons. Most Promethium atoms have about 84 neutrons: the atomic mass rounded to 145, minus the atomic number 61.
Neutrons are approximate: atoms of the same element can have different numbers of neutrons (isotopes). Atomic number and mass
How many valence electrons does Promethium have?
2
Promethium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.
Promethium 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 Promethium
145 g/mol
One mole of Promethium atoms (6.022 × 10²³ atoms) has a mass of 145 grams. Use this value to convert between grams and moles.
Promethium facts
- Promethium is the only lanthanide with no stable isotopes, so almost none of it exists naturally on Earth.
- Before 1945, several groups claimed to have found element 61, naming it illinium or florentium, but none of the claims held up.
- Promethium (Pm) has atomic number 61 and is a solid at room temperature. It was discovered in 1945.
Position in the periodic table
Promethium is element 61, in period 6 of the periodic table. It is one of the Lanthanides in the f-block, shown in the rows below the main table.
Uses of Promethium
Promethium has very few uses because all its isotopes are radioactive and it is extremely rare. Promethium-147 has been used in nuclear batteries for some early heart pacemakers, in luminous paint for watch dials, and in gauges that measure the thickness of materials. Today it is mainly a subject of scientific research.
Who discovered Promethium?
Jacob Marinsky, Lawrence Glendenin, and Charles Coryell identified promethium in 1945 at Clinton Laboratories (now Oak Ridge National Laboratory) in Tennessee, by separating it from the fission products of uranium. It was named after Prometheus, the Titan who stole fire from the gods.
Where does the name come from?
Promethium is named after Prometheus, the Titan in Greek mythology who stole fire from the gods and gave it to humans. Grace Mary Coryell, wife of one of its discoverers, suggested the name as a symbol of both human daring and its dangers.
Lanthanide
Compare Promethium
FAQ
What is the electron configuration of Promethium?
The electron configuration of Promethium (Pm) is [Xe] 4f5 6s2. Its 61 electrons are arranged in shells as 2, 8, 18, 23, 8, 2.
How many protons, neutrons and electrons does Promethium have?
A neutral Promethium atom has 61 protons and 61 electrons. Most Promethium atoms have about 84 neutrons: the atomic mass rounded to 145, minus the atomic number 61.
How many valence electrons does Promethium have?
Promethium has 2 valence electrons in its outermost shell. As an f-block element, its 4f or 5f electrons can also take part in bonding.
What is the molar mass of Promethium?
The molar mass of Promethium is 145 g/mol. This is the same number as its atomic mass, 145 u.
Is Promethium a metal?
Yes. Promethium is a lanthanide, so it is a metal.
Is Promethium radioactive?
Yes. Promethium has no stable isotopes, so all of its atoms are radioactive and eventually decay into other elements.
Where is Promethium on the periodic table?
Promethium is element 61, in period 6 of the periodic table. It is one of the Lanthanides in the f-block, shown in the rows below the main table.