# Question #d9894

##### 1 Answer

#### Explanation:

I assume that you're interested in finding an ion that has a **4+** charge and the electron configuration

#"X"^(4+): ["Ar"] 4s^0 3d^3#

A very important thing to notice here is tha tyou're dealing with a *transition metal*.

Why is this important?

Because you know that transition metals have the *4s-orbital* **higher in energy** than the *3d-orbitals*.

This implies that when the cation is formed, the first electrons removed from the ion will come from the **4s-orbital**, not from the 3d-orbitals.

Now, notice that you have *empty*.

You can reform the atom by adding electrons to the cation. This will help you figure out what ion you started with.

So, the first electron **added** to this ion will be placed in a 3d-orbital, since these are *lower in energy*. This means that you have

#"X"^(3+): ["Ar"] 4s^0 3d^4#

The second electron added will also be placed in the 3d-orbitals

#"X"^(2+): ["Ar"] 4s^0 3d^5#

The **third** and **fourth** electrons **must** occupy the 4s-orbital because you know that this orbital was emptied first when the cation was formed. This means that you have.

#"X"^(+): ["Ar"] 4s^1 3d^4" "# and#" ""X": ["Ar"] 4s^2 3d^4#

The electron configuration of atom

#["Ar"] 4s^2 3d^5#

Since *neutral atom*, its atomic number will be **equal** to the number of electrons it has surrounding its nucleus.

Argon has **18** electrons surrounding its nucleus, which means that your atom will have

#18 + 2 + 5 = "25 e"""^(-)#

Therefore, the neutral atom **manganese**, **25** electrons surrounding its nucleus.

This implies that