Question

What is the electron configuration of `"Ti"^(2+)`?

Answer 1

`"Ti"^(2+): ["Ar"]3d^2`

Explanation:

A good place to start when trying to figure out the electron configuration of an ion is the electron configuration of the neutral parent atom.

In this case, titanium, `"Ti"`, is located in period 4, group 4 of the periodic table and has an atomic number of `22`.

This means that a neutral titanium atom will contain `22` protons in its nucleus and `22` electrons surrounding its nucleus.

Therefore, the electron configuration of a neutral titanium atom must account for `22` electrons. Consequently, the electron configuration of the titanium(II) cation, `"Ti"^(2+)`, must account for `20` electrons, since this cation is formed when a neutral titanium atom loses `2` electrons.

The electron configuration of a neutral titanium atom looks like this

`"Ti: " 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^2`

Now, it's important to keep in mind that this notation for the electron configuration is useful when adding electrons to build an atom "from scratch" because in that case, the `4s` orbital is filled before the `3d` orbitals.

That happens because the empty `3d` orbitals are actually higher in energy than the empty `4s` orbital, as seen here

However, once the `4s` orbital is filled, it becomes higher in energy than the `3d` orbitals. This means that when titanium loses electrons, it does so from the `4s` orbital first.

`"Ti: " 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2 4s^2`

Therefore, the two electrons that are lost when the `"Ti"^(2+)` is formed will come from the `4s` orbital, which means that the electron configuration of the cation is

`color(green)(|bar(ul(color(white)(a/a)color(black)("Ti"^(2+): 1s^2 2s^2 2p^6 3s^2 3p^6 3d^2)color(white)(a/a)|)))`

If you want, you can use the noble gas shorthand notation to write

`color(green)(|bar(ul(color(white)(a/a)color(black)("Ti"^(2+): ["Ar"] 3d^2)color(white)(a/a)|)))`

Here `["Ar"]` represents the electron configuration of argon, the noble gas that comes immediately before titanium in the periodic table.