Write the ground state electronic configurations, and indicate the number of unpaired electrons, for: (a) Ti (titanium); (b) Ti2+; (c) Ti3+; (d) the first excited state of Ne; (e) the as-yet undiscovered alkali metal that would begin the 8th row of the periodic table (under Fr):
The Correct Answer and Explanation is:
Here is the correct answer for each part:
(a) Titanium (Ti)
- Atomic number: 22
- Ground state electron configuration:
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d² - Number of unpaired electrons: 2 (in 3d²)
(b) Titanium ion (Ti²⁺)
- Electron configuration after removing 2 electrons from neutral Ti:
1s² 2s² 2p⁶ 3s² 3p⁶ 3d² (4s electrons are lost first) - Number of unpaired electrons: 2 (in 3d²)
(c) Titanium ion (Ti³⁺)
- Electron configuration after removing 3 electrons from neutral Ti:
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ - Number of unpaired electrons: 1 (in 3d¹)
(d) First excited state of neon (Ne)
- Ground state configuration of Ne (atomic number 10):
1s² 2s² 2p⁶ (all orbitals filled) - First excited state:
An electron from the 2p orbital is promoted to 3s: 1s² 2s² 2p⁵ 3s¹ - Number of unpaired electrons: 2 (one in 2p and one in 3s)
(e) Alkali metal beginning the 8th row (element 119, under Francium)
- Expected ground state electron configuration:
[Og] 8s¹ - Number of unpaired electrons: 1 (in 8s¹)
Explanation
Electron configurations describe the arrangement of electrons in an atom’s orbitals, following the Aufbau principle, Hund’s rule, and the Pauli exclusion principle. In a neutral titanium (Ti) atom, the 22 electrons fill up orbitals in increasing energy levels. The configuration ends with 4s² 3d², with two unpaired electrons in the 3d subshell.
For ions, electrons are removed from the outermost shells first. In Ti²⁺, the two 4s electrons are lost, leaving 3d² with two unpaired electrons. In Ti³⁺, one additional electron is removed from the 3d orbital, resulting in a 3d¹ configuration with one unpaired electron.
In neon, which has a closed-shell configuration, the ground state has all electrons paired. An excited state is formed by promoting an electron from a filled orbital (like 2p) to a higher orbital (like 3s). This excited state introduces unpaired electrons where previously all were paired, increasing reactivity and energy.
The hypothetical alkali metal in the 8th period would continue the periodic pattern. Alkali metals always have a single electron in their outermost s-orbital. For element 119, this electron would be in the 8s orbital, resulting in an [Og] 8s¹ configuration. Like all alkali metals, it would have one unpaired electron, contributing to its high reactivity.
Understanding electron configurations helps explain chemical reactivity, bonding behavior, and magnetic properties based on how electrons are arranged and whether they are paired or not.
