Rutherfordium at a glance
- Atomic number
- 104
- Symbol
- Rf
- Atomic mass
- 267 u
- Category
- Transition metal
- Group / period
- 4 / 7
- Electron configuration
- [Rn] 5f 14 6d 2 7s 2
- State at 25 °C
- Unknown
- Melting point
- n/a
- Boiling point
- n/a
- Density
- 17 g/cm³
- Electronegativity
- n/a
- 1st ionization energy
- 580 kJ/mol
- Oxidation states
- +4 (pred.)
- Discovered
- 1964
Atomic structure
A neutral rutherfordium atom has 104 protons and 104 electrons, and its most common isotope carries about 163 neutrons. One atom weighs about 4.43 × 10⁻²⁵ kg, so a mole of rutherfordium (6.022 × 10²³ atoms) weighs 267 g. That nucleus holds 1.57 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 7 shells (K 2, L 8, M 18, N 32, O 32, P 10, Q 2), which gives the configuration [Rn] 5f 14 6d 2 7s 2. As a d-block element, both its outer s electrons and its inner d electrons can take part in bonding, which is why it shows more than one oxidation state. Every isotope is radioactive and short-lived; only a handful of atoms have ever been made, one at a time.
Physical properties
So little rutherfordium has ever existed at once that its melting point, boiling point and even its state at room temperature are unknown. Its density is 17 g/cm³ (predicted), 17 times as dense as water.
Chemical behaviour
It has no measured electronegativity. Pulling off its outermost electron takes 580 kJ/mol (predicted), less than Hafnium above it (659 kJ/mol). Group 4 also holds Titanium, Zirconium and Hafnium, which share its outer-shell pattern. Handle with care: as a pure element it is radioactive.
Where it comes from
It does not occur in nature in useful amounts; it is made in nuclear reactors or particle accelerators. It was first made at Dubna and at Berkeley, which both claimed it by fusing plutonium with neon, or californium with carbon. Its longest-lived known isotope is Rf-267, about 1.3 hours. It was first identified in 1964, making it the 104th element to be discovered (counting the 11 known since antiquity together).