Praseodymium at a glance
- Atomic number
- 59
- Symbol
- Pr
- Atomic mass
- 140.91 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 3 6s 2
- State at 25 °C
- Solid
- Melting point
- 934.9 °C
- Boiling point
- 3520 °C
- Density
- 6.773 g/cm³
- Electronegativity
- 1.13
- 1st ionization energy
- 527 kJ/mol
- Oxidation states
- +3
- Discovered
- 1885
Atomic structure
A neutral praseodymium atom has 59 protons and 59 electrons, and its most common isotope carries about 82 neutrons. One atom weighs about 2.34 × 10⁻²⁵ kg, so a mole of praseodymium (6.022 × 10²³ atoms) weighs 140.91 g. That nucleus holds 1.39 neutrons for every proton. The electrons fill 6 shells (K 2, L 8, M 18, N 21, O 8, P 2), which gives the configuration [Xe] 4f 3 6s 2. As a f-block element, both its outer s electrons and its inner f electrons can take part in bonding, which is why it shows more than one oxidation state. It has only one stable isotope, Pr-141. No other element has a stable isotope with mass number 141, so Pr-141 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) praseodymium is a solid. It melts at 934.9 °C and boils at 3520 °C, so it stays liquid across a 2585-degree range. It stays solid in a hot kitchen oven but would melt in a candle flame (about 1000 °C). Its density is 6.773 g/cm³, 6.77 times as dense as water. Its atoms have a radius of about 185 pm (Cerium next door is 185 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.13 on the Pauling scale. Pulling off its outermost electron takes 527 kJ/mol. A bond between praseodymium and chlorine would be mostly ionic, with an electronegativity difference of 2. Its common oxidation states are +3, so in compounds you will usually meet it as Pr³⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Lanthanum, Cerium, Neodymium and Promethium.
Where it comes from
It makes up 9.2 mg/kg of Earth's crust, the 39th most abundant element there. It was first identified in 1885, making it the 71st element to be discovered (counting the 11 known since antiquity together).