Ionisation Energy Order of Ti, Zr, Hf

To determine the ionization energy order of Ti, Zr, and Hf, we need to understand the concept of ionization energy and the factors that influence it.

Ionization Energy:
Ionization energy refers to the energy required to remove an electron from an atom or ion in its gaseous state. It is typically measured in kilojoules per mole (kJ/mol) or electron volts (eV). The ionization energy generally increases as we move across a period in the periodic table and decreases as we move down a group.

Factors Affecting Ionization Energy:
Several factors influence the ionization energy of an element, including:
1. Nuclear charge: The greater the nuclear charge, the stronger the attraction between the nucleus and the electrons, resulting in higher ionization energy.
2. Atomic radius: The smaller the atomic radius, the closer the valence electrons are to the nucleus, leading to higher ionization energy.
3. Electron shielding: The presence of inner electrons shields the valence electrons from the attraction of the nucleus, reducing the ionization energy.
4. Penetration effect: Electrons in higher energy orbitals have greater penetration into the region occupied by the lower energy orbitals, resulting in lower ionization energy.

Ionization Energy Order:
Based on the mentioned factors, we can determine the ionization energy order of Ti, Zr, and Hf:

1. Titanium (Ti):
- Atomic number: 22
- Ti has 22 electrons, with the electronic configuration [Ar] 3d^2 4s^2.
- The removal of the first electron from Ti involves the 4s orbital, which is further from the nucleus compared to the 3d orbital.
- The electron being removed experiences less nuclear attraction, making it easier to remove.
- Therefore, the first ionization energy of Ti is relatively low.

2. Zirconium (Zr):
- Atomic number: 40
- Zr has 40 electrons, with the electronic configuration [Kr] 4d^2 5s^2.
- The removal of the first electron from Zr involves the 5s orbital, which is slightly closer to the nucleus compared to the 4d orbital.
- The electron being removed experiences greater nuclear attraction, resulting in a higher first ionization energy compared to Ti.

3. Hafnium (Hf):
- Atomic number: 72
- Hf has 72 electrons, with the electronic configuration [Xe] 4f^14 5d^2 6s^2.
- The removal of the first electron from Hf involves the 6s orbital, which is closer to the nucleus compared to the 5d orbital.
- The electron being removed experiences even greater nuclear attraction, leading to a higher first ionization energy compared to both Ti and Zr.

Ionization Energy Order:
Based on the factors discussed above, the ionization energy order of Ti, Zr, and Hf can be summarized as follows:

1. Lowest ionization energy: Titanium (Ti)
2. Intermediate ionization energy: Zirconium (Zr)
3. Highest ionization energy: Hafnium (Hf)

Therefore,