Write the ground state isoelectronic partner of the following elements – Ti3+ a) Ca b) Sc c) K
The Correct Answer and Explanation is:
Correct Answer: a) Ca
Explanation:
The term isoelectronic refers to atoms, ions, or molecules that have the same number of electrons and hence the same electronic configuration in their ground state.
Let’s first find the electronic configuration of the ion Ti³⁺ (Titanium 3+).
- Atomic number of Titanium (Ti) = 22
- Neutral Ti: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d² 4s²
- When Ti loses 3 electrons to form Ti³⁺, electrons are removed first from the 4s orbital and then from the 3d orbital:
Ti³⁺ = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹
So, Ti³⁺ has 19 electrons.
We are to find which neutral element has 19 electrons as well. The number of electrons in a neutral atom equals its atomic number.
- a) Calcium (Ca): Atomic number 20 → 20 electrons
- b) Scandium (Sc): Atomic number 21 → 21 electrons
- c) Potassium (K): Atomic number 19 → 19 electrons
So the element with 19 electrons is Potassium (K).
However, the question is asking for the ground state isoelectronic partner, which means an atom or ion that has the same electron configuration as Ti³⁺ in its ground state.
Let’s compare:
- Ti³⁺ has an electronic configuration ending in 3d¹.
- Potassium (K) in its neutral form has configuration [Ar] 4s¹, not isoelectronic with Ti³⁺.
- Calcium (Ca²⁺) would be [Ar], which is 18 electrons.
- Calcium (Ca) in neutral form has 20 electrons, configuration [Ar] 4s², but when it loses 1 electron (Ca⁺), it has 19 electrons.
But here, the neutral atom with 19 electrons is Potassium (K).
However, their electron configurations are different:
- Ti³⁺: [Ar] 3d¹
- K: [Ar] 4s¹
Therefore, the correct isoelectronic partner of Ti³⁺ should have an electron configuration [Ar] 3d¹.
This matches the ground state of Scandium (Sc²⁺), which is not among the choices.
But among the neutral atoms listed in the options, none are truly isoelectronic in terms of full configuration match.
Hence, the best match among the given neutral elements in terms of electron count only is:
Correct answer: c) K
Because both Ti³⁺ and K have 19 electrons, even though their orbital arrangement is different due to ionization and energy level differences.
So, the correct isoelectronic partner by electron count is Potassium (K).
