# Effective atomic number of #Fe# in #Fe_"2"(CO)_"9"# is ??

##### 1 Answer

It would be

You can also find a worked effective atomic number example here.

The **effective atomic number** corresponds to the total number of electrons around the transition metal given by the ligands, PLUS the *total* number of electrons the transition metal brings.

Two methods are common to find the electrons donated by the ligands, which I will call:

- the
**Donor Pair method**(Method A) - the
**Neutral Ligand method**(Method B)

**THE DONOR PAIR METHOD**

This method considers the ligand to donate a lone pair of electrons, and assigns the charges and atomic oxidation states accordingly. So, **two** electrons.

**THE NEUTRAL LIGAND METHOD**

This method considers the ligand to give as many electrons for the bond as it would have if it were neutral. So, **one** electron.

The following table lists the number of donated electrons considered using both methods:

**EXAMINING**

Since this compound is symmetric about the vertical mirror plane perpendicular to the screen (the plane perpendicular to the

In the case of

#:"C"-="O":#

It has a lone pair, and it is neutral, so it donates two electrons under either method. The **a given**

#6 xx 2 = bb12# electrons

to the effective atomic number.

**oxidation state** of *no charge*, and both iron atoms must be *identical oxidation states* by symmetry.

Thus, **electrons** to the effective atomic number, as it is neutral and has an atomic number of

That means its **effective atomic number** is

#6 xx 2 + 26 = color(blue)bb(38)#