Titanium at a glance
- Atomic number
- 22
- Symbol
- Ti
- Atomic mass
- 47.867 u
- Category
- Transition metal
- Group / period
- 4 / 4
- Electron configuration
- [Ar] 3d 2 4s 2
- State at 25 °C
- Solid
- Melting point
- 1668 °C
- Boiling point
- 3287 °C
- Density
- 4.54 g/cm³
- Electronegativity
- 1.54
- 1st ionization energy
- 659 kJ/mol
- Oxidation states
- +4, +3
- Discovered
- 1791
Atomic structure
A neutral titanium atom has 22 protons and 22 electrons, and its most common isotope carries about 26 neutrons. One atom weighs about 7.95 × 10⁻²⁶ kg, so a mole of titanium (6.022 × 10²³ atoms) weighs 47.867 g. That nucleus holds 1.18 neutrons for every proton. The electrons fill 4 shells (K 2, L 8, M 10, N 2), which gives the configuration [Ar] 3d 2 4s 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 5 stable isotopes: Ti-46, Ti-47, Ti-48, Ti-49 and Ti-50. Its most common isotope, Ti-48, has the same mass number as Ca-48: isobars, nuclei of different elements with 48 nucleons each.
Physical properties
At room temperature (25 °C) titanium is a solid. It melts at 1668 °C and boils at 3287 °C, so it stays liquid across a 1619-degree range. It stays solid in molten iron (1538 °C) but would melt in a welding arc. Its density is 4.54 g/cm³, 4.54 times as dense as water. Its atoms have a radius of about 140 pm (Scandium next door is 160 pm). In the solid, its atoms pack into a hexagonal close-packed lattice.
Chemical behaviour
Its electronegativity is 1.54 on the Pauling scale. Pulling off its outermost electron takes 659 kJ/mol. A bond between titanium and chlorine would be polar covalent, with an electronegativity difference of 1.6. It releases 8 kJ/mol when it gains an extra electron. Its common oxidation states are +4, +3, so in compounds you will usually meet it as Ti⁴⁺ and Ti³⁺. Group 4 also holds Zirconium, Hafnium and Rutherfordium, which share its outer-shell pattern.
Where it comes from
It makes up 5650 mg/kg of Earth's crust, the 9th most abundant element there. It was first identified in 1791, making it the 30th element to be discovered (counting the 11 known since antiquity together).