Gadolinium at a glance
- Atomic number
- 64
- Symbol
- Gd
- Atomic mass
- 157.25 u
- Category
- Lanthanide
- Period
- 6
- Electron configuration
- [Xe] 4f 7 5d 1 6s 2
- State at 25 °C
- Solid
- Melting point
- 1312 °C
- Boiling point
- 3273 °C
- Density
- 7.895 g/cm³
- Electronegativity
- 1.2
- 1st ionization energy
- 593 kJ/mol
- Oxidation states
- +3
- Discovered
- 1880
Atomic structure
A neutral gadolinium atom has 64 protons and 64 electrons, and its most common isotope carries about 94 neutrons. One atom weighs about 2.61 × 10⁻²⁵ kg, so a mole of gadolinium (6.022 × 10²³ atoms) weighs 157.25 g. That nucleus holds 1.47 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 6 shells (K 2, L 8, M 18, N 25, O 9, P 2), which gives the configuration [Xe] 4f 7 5d 1 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. Its configuration breaks the simple filling order: one electron moves so that a subshell becomes half-full or full, which is more stable. It has 6 stable isotopes: Gd-154, Gd-155, Gd-156, Gd-157, Gd-158 and Gd-160. Its most common isotope, Gd-158, has the same mass number as Dy-158: isobars, nuclei of different elements with 158 nucleons each.
Physical properties
At room temperature (25 °C) gadolinium is a solid. It melts at 1312 °C and boils at 3273 °C, so it stays liquid across a 1961-degree range. It stays solid in a candle flame (about 1000 °C) but would melt in molten iron (1538 °C). Its density is 7.895 g/cm³, 7.89 times as dense as water. Its atoms have a radius of about 180 pm (Europium next door is 185 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.2 on the Pauling scale. Pulling off its outermost electron takes 593 kJ/mol. A bond between gadolinium 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 Gd³⁺. It shares much of its chemistry with the other lanthanides, especially its neighbours Samarium, Europium, Terbium and Dysprosium.
Where it comes from
It makes up 6.2 mg/kg of Earth's crust, the 41st most abundant element there. It was first identified in 1880, making it the 70th element to be discovered (counting the 11 known since antiquity together).