Draw the Lewis structure of the phosphite polyatomic ion, PO3^3- and answer the following questions in your uploaded file: A) Total number of valence electrons = B) Central atom (symbol or name or element) = C) Pairs of unshared electrons on the central atom = D) Pairs of unshared electrons in the entire structure = E) Polarity of the ion (polar or nonpolar) = F) Electron domain geometry = G) Molecular geometry =
The Correct Answer and Explanation is:
Lewis Structure of Phosphite Ion (PO₃³⁻)
To draw the Lewis structure and answer the questions, let us go step-by-step:
A) Total number of valence electrons = 26
- Phosphorus (P) has 5 valence electrons.
- Each oxygen (O) has 6 valence electrons.
- There are 3 oxygen atoms, so 3 × 6 = 18 electrons.
- The ion has a charge of 3−, so we add 3 more electrons.
Total = 5 (P) + 18 (O) + 3 (charge) = 26 valence electrons
B) Central atom = P (Phosphorus)
Phosphorus is less electronegative than oxygen, so it is placed in the center.
C) Pairs of unshared electrons on the central atom = 1
After forming single bonds with three oxygens and completing their octets, phosphorus has one lone pair (2 electrons) left on it.
D) Pairs of unshared electrons in the entire structure = 10
- Each oxygen atom has 3 lone pairs = 3 × 3 = 9 pairs
- Phosphorus has 1 lone pair
- Total = 9 + 1 = 10 pairs
E) Polarity of the ion = Polar
The shape is trigonal pyramidal, and due to the lone pair on phosphorus, the molecule is not symmetric, leading to a net dipole moment.
F) Electron domain geometry = Tetrahedral
There are four regions of electron density around phosphorus (three bonding pairs and one lone pair), giving a tetrahedral electron geometry.
G) Molecular geometry = Trigonal pyramidal
With three bonded atoms and one lone pair on phosphorus, the resulting shape is trigonal pyramidal.
Explanation:
The phosphite ion (PO₃³⁻) is a polyatomic ion containing one phosphorus atom and three oxygen atoms, with an overall charge of minus three. To draw its Lewis structure, we start by counting the total number of valence electrons: phosphorus has 5, each oxygen contributes 6, and the negative charge adds 3 more electrons, giving a total of 26 valence electrons.
Phosphorus is placed at the center because it is the least electronegative atom. Each of the three oxygen atoms is bonded to phosphorus with a single bond. This arrangement uses 6 electrons for bonding (3 single bonds × 2 electrons each = 6). The remaining 20 electrons are used to complete the octets of the oxygen atoms (each receiving 6 more to reach 8). After distributing electrons to the oxygens, phosphorus ends up with one lone pair of electrons, satisfying its own octet.
The shape of the ion is determined by the electron groups around phosphorus. Since it has three bonding pairs and one lone pair, the electron domain geometry is tetrahedral. However, the lone pair pushes the bonds downward, making the molecular geometry trigonal pyramidal. Because of this lone pair and the difference in electronegativity between phosphorus and oxygen, the structure is polar.
There are 10 lone pairs in total: three oxygens with three pairs each (9) and one lone pair on phosphorus. The negative charge is delocalized, often shown using resonance, especially if one oxygen forms a double bond.
This structure and its geometry help explain the chemical behavior of the phosphite ion in various reactions.
