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

Jun 27, 2016

"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, $\text{Ti}$, 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, ${\text{Ti}}^{2 +}$, 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

$\text{Ti: } 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 4 {s}^{2} 3 {d}^{2}$

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 $4 s$ orbital is filled before the $3 d$ orbitals.

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

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

$\text{Ti: } 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{2} 4 {s}^{2}$

Therefore, the two electrons that are lost when the ${\text{Ti}}^{2 +}$ is formed will come from the $4 s$ orbital, which means that the electron configuration of the cation is

$\textcolor{g r e e n}{| \overline{\underline{\textcolor{w h i t e}{\frac{a}{a}} \textcolor{b l a c k}{{\text{Ti}}^{2 +} : 1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{2}} \textcolor{w h i t e}{\frac{a}{a}} |}}}$

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 $\left[\text{Ar}\right]$ represents the electron configuration of argon, the noble gas that comes immediately before titanium in the periodic table.