The Atomic Structure of Titanium
Titanium (Ti) is a chemical element renowned for its high strength-to-density ratio, corrosion resistance, and metallic lustre. It is a transition metal, often found in minerals like ilmenite and rutile, which are mined in various parts of the world, including the extensive beach sands of Kerala, Tamil Nadu, and Odisha in India. Its unique properties make it invaluable in numerous applications, from aerospace components to medical implants and pigments. Understanding its atomic structure is fundamental to comprehending its chemical behaviour.
Atomic Composition
The atomic structure of a neutral titanium atom can be described by the number of its constituent particles: protons, neutrons, and electrons.
- Atomic Number (Z): Titanium has an atomic number of 22. This number defines the element and represents the count of protons in the nucleus of every titanium atom.
- Number of Protons: 22
- Number of Electrons: In a neutral atom, the number of electrons orbiting the nucleus is equal to the number of protons.
- Number of Electrons: 22
- Mass Number (A): The most common isotope of titanium is Titanium-48 ($\text{Ti}^{48}$), which has a mass number of 48. The mass number is the sum of protons and neutrons in the nucleus.
- Number of Neutrons: Calculated by subtracting the atomic number from the mass number (A - Z = 48 - 22).
- Number of Neutrons: 26 (for the most common isotope, $\text{Ti}^{48}$)
Electron Configuration
Electron configuration describes the distribution of electrons of an atom in atomic orbitals. For titanium (atomic number 22), the 22 electrons occupy the available energy levels and orbitals according to the Aufbau principle, Pauli exclusion principle, and Hund’s rule.
The full electron configuration for a neutral titanium atom is: $\text{1s}^2 \text{2s}^2 \text{2p}^6 \text{3s}^2 \text{3p}^6 \text{3d}^2 \text{4s}^2$
This can also be written in a shorthand notation using the preceding noble gas, Argon (Ar), which has 18 electrons: $[\text{Ar}] \text{3d}^2 \text{4s}^2$
This configuration indicates that the first 18 electrons fill the orbitals up to the 3p subshell, identical to an Argon atom. The remaining four electrons occupy the 3d and 4s subshells. It is common practice to list the subshells in increasing principal quantum number order, even if the 4s subshell fills before the 3d subshell.
Valence Electrons
Valence electrons are the electrons located in the outermost shell or the highest principal energy level of an atom. These electrons are primarily involved in chemical bonding. For transition metals like titanium, both the electrons in the outermost s-orbital and the partially filled (n-1)d orbitals contribute to the atom’s chemical reactivity.
For titanium, the electron configuration $[\text{Ar}] \text{3d}^2 \text{4s}^2$ shows:
- The 4s subshell is the outermost energy level (n=4) containing 2 electrons.
- The 3d subshell (n=3) is partially filled and contains 2 electrons.
Therefore, titanium typically has 4 valence electrons (2 from the 4s orbital and 2 from the 3d orbital) that participate in forming chemical bonds, explaining its common oxidation states, such as +2, +3, and +4.