Tantalum at a glance
- Atomic number
- 73
- Symbol
- Ta
- Atomic mass
- 180.95 u
- Category
- Transition metal
- Group / period
- 5 / 6
- Electron configuration
- [Xe] 4f 14 5d 3 6s 2
- State at 25 °C
- Solid
- Melting point
- 3017 °C
- Boiling point
- 5458 °C
- Density
- 16.65 g/cm³
- Electronegativity
- 1.5
- 1st ionization energy
- 761 kJ/mol
- Oxidation states
- +5
- Discovered
- 1802
Atomic structure
A neutral tantalum atom has 73 protons and 73 electrons, and its most common isotope carries about 108 neutrons. One atom weighs about 3 × 10⁻²⁵ kg, so a mole of tantalum (6.022 × 10²³ atoms) weighs 180.95 g. That nucleus holds 1.48 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 32, O 11, P 2), which gives the configuration [Xe] 4f 14 5d 3 6s 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. It has only one stable isotope, Ta-181. No other element has a stable isotope with mass number 181, so Ta-181 has no stable isobars; its neighbours on that line decay into it or away from it.
Physical properties
At room temperature (25 °C) tantalum is a solid. It melts at 3017 °C and boils at 5458 °C, so it stays liquid across a 2441-degree range. It stays solid in molten iron (1538 °C) but would melt in a welding arc. That is the 5th highest melting point of any element. Its density is 16.65 g/cm³, 16.7 times as dense as water. Its atoms have a radius of about 145 pm (Hafnium next door is 155 pm). In the solid, its atoms pack into a body-centred cubic lattice.
Chemical behaviour
Its electronegativity is 1.5 on the Pauling scale. Pulling off its outermost electron takes 761 kJ/mol, more than Niobium above it (652 kJ/mol). A bond between tantalum and chlorine would be polar covalent, with an electronegativity difference of 1.7. It releases 31 kJ/mol when it gains an extra electron. Its common oxidation states are +5, so in compounds you will usually meet it as Ta⁵⁺. Group 5 also holds Vanadium, Niobium and Dubnium, which share its outer-shell pattern.
Where it comes from
It makes up 2 mg/kg of Earth's crust, the 53rd most abundant element there. It was first identified in 1802, making it the 36th element to be discovered (counting the 11 known since antiquity together).