which of the lewis electron dot representations is correct for the phosphite ion, po₃⁻³?

Answer:

The correct Lewis - electron dot representation is the one on the right.

Explanation:

Step1: Calculate valence electrons

Phosphorus (P) has 5 valence electrons, oxygen (O) has 6 valence electrons. For $PO_{3}^{-3}$, the total number of valence electrons is $5 + 3\times6+3=26$ electrons.

Step2: Analyze left structure

In the left - hand structure with a P = O double bond, the formal charge on P is $5-(4 + 2)= - 1$ and on the double - bonded O is $6-(4 + 2)=0$, and on single - bonded O is $6-(6 + 1)= - 1$. The sum of formal charges is $-1+0 + 2\times(-1)=-3$. But the double bond makes the structure less stable as it violates the octet rule for P in a way that is not the most stable resonance form for this ion.

Step3: Analyze right structure

In the right - hand structure, all atoms have a more stable formal charge distribution. The formal charge on P is $5-(6 + 1)= - 2$ and on each O is $6-(6 + 1)= - 1$. The sum of formal charges is $-2+3\times(-1)=-3$. Also, all atoms follow the octet rule, and this is the more stable Lewis structure for the phosphite ion $PO_{3}^{-3}$.