To draw the Lewis dot structure for phosphorous acid (H3PO3), we start by determining the total number of valence electrons available. Hydrogen has 1 valence electron and contributes a total of 3 for H3, while phosphorus (P) has 5 valence electrons, and each oxygen (O) has 6 valence electrons. Thus, for H3PO3:
3 (H) + 5 (P) + 3 × 6 (O) = 3 + 5 + 18 = 26 valence electrons.
We begin by placing the phosphorus atom in the center since it’s less electronegative than oxygen. Then we attach the three hydrogen atoms and the three oxygen atoms to phosphorus. To ensure that all atoms achieve a stable electron configuration, we arrange the atoms as follows:
1. Phosphorus is central with three hydrogens attached.
2. Two of the oxygens will have single bonds with phosphorus, and one will have a double bond.
3. Oxygen atoms will hold two lone pairs (if single bonded) or one lone pair (if double bonded).
This arrangement allows phosphorus to have a total of 8 electrons (following the octet rule), satisfying all atoms involved. Essentially, the Lewis structure of H3PO3 looks like this:
H
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H – O – P = O
|
H
In this Lewis structure, phosphorus forms one double bond with one oxygen atom and single bonds with two hydrogen and one other oxygen atom. The double bond represents a stronger bond compared to the single bonds, ensuring that phosphorus achieves its stable configuration. Each hydrogen is attached directly to phosphorus and is bonded through a single bond.
This structure not only illustrates the distribution of electrons but also conveys the molecular geometry of phosphorous acid, which is essential for understanding its chemical behavior.