Question

consider the structure below for the eof₂²⁻ ion. note: e represents an unidentified element.
(a) what is the formal charge on e?
(b) which element could e represent? (although there is more than one possibility, you must enter only one answer. enter the correct atomic symbol for your choice.)

Explanation:

Step1: Calculate the formal charge on E

The formula for formal charge is \(FC = V - N - \frac{B}{2}\), where \(V\) is the number of valence electrons of the atom in its neutral state, \(N\) is the number of non - bonding electrons, and \(B\) is the number of bonding electrons.
Assume \(E\) has \(V\) valence electrons. From the structure, \(E\) has \(N = 0\) non - bonding electrons (since there are no lone pairs shown on \(E\) in the bonding picture), and \(B=8\) (two single bonds and one double bond, each single bond has 2 electrons and double bond has 4 electrons, \(2 + 2+4=8\)).
Let's assume \(E\) is in group 16 (since it forms bonds in this structure). For a group 16 element, \(V = 6\).

$$FC=6 - 0-\frac{8}{2}=6 - 4= + 2$$

Step2: Determine the element \(E\)

The ion is \([EOF_{2}]^{2-}\). The total charge of the ion is \(- 2\). Let the charge of \(E\) be \(x\), charge of \(O=-2\) (in this bonding situation, oxygen has a formal charge of \(- 2\) as it has 6 valence electrons, 6 non - bonding electrons (\(N = 6\)) and 2 bonding electrons (\(B = 2\)), \(FC_O=6 - 6-\frac{2}{2}=-1\), but considering the overall ion charge, using the formula for the charge of the ion: \(x+(-2)+2\times(-1)=-2\) (where \(x\) is the charge of \(E\), \(-2\) is the charge of \(O\) and \(-1\) is the charge of each \(F\)).

$$x-2 - 2=-2\Rightarrow x = + 2$$

An element that can have a + 2 formal charge and form such a structure. Selenium (\(Se\)) is a group 16 element that can expand its octet (similar to sulfur) and form such a structure.

Answer:

(a) \(+2\)
(b) \(Se\)