Lewis structure of hypophosphorous acid (H3PO2) can be built by following rules of VSEPR theory. When, drawing the lewis structure there are requirements to be satisfied. Charges of atoms should be minimized in the lewis structure of H3PO2 to be a stable structure.
Hypophosphorous acid is a monobasic weak acid. It means, it can release only single hydrogen atoms to show acidic characteristics. Therefore, we can assume, there should be one -OH bonds in phosphorous acid molecule.
Most stable and probable lewis structure of H3PO2 is shown below. In the lewis structure of H3PO2, there is a double bond between phosphorous atom and oxygen atom, two P-H bonds and one O-H bond.
Following steps are followed to draw the H3PO2 lewis structure. Those steps are explained in detail in next sections. If you are are beginner to lewis structure construction, follow these sections slowly and properly to understand it completely.
Drawing the correct lewis structure is important to draw resonance structures correctly
Phosphorous is a group VA element. Therefore, it has five electrons in its valence shell. Oxygen has six electrons in its last shell because it is a group VIA element. Hydrogen has only one electron in its valence shell. To find number of valence electron , these valence electrons of each element should be multiplied with their respective number of atoms in the molecule. Below, That step is done.
There are three oxygen atoms in H3PO2 molecule, Therefore
There are three hydrogen atoms in H3PO2 molecule, Therefore
There are no charges in H3PO2 molecule.
Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells
Total electron pairs are determined by dividing the number total valence electrons by two. For, H3PO2 molecule, Total number of pairs of electrons are 10.
There are some requirements to be the center atom. Having a high valence is a main requirement to be a center atom. For H3PO2 molecule, phosphorous has the highest valence than oxygen and hydrogen.
Because, hypophosphorous acid is a monobasic acid, it can release two H+ ions in the water. Therefore, there should be two -OH groups in H3PO3 molecule. Therefore, we can present following sketch for H3PO2 molecule.
After drawing the sketch, we should start to mark lone pairs on atoms.
Charges on atoms is important to find the most stable lewis structure. Therefore, we should try to find charges if there are.
After, marking electron pairs on atoms, we should mark charges of each atom. One oxygen atoms will get a -1 charge and phosphorous atom get a +1 charge. Hypophosphorous acid is a neutral molecule and overall charge should be zero. The overall charge of th e molecule is ( -1*1 + (+1) ) = 0.
When charges exist on lot of atoms in an ion or molecule, that structure is not stable. Therefore, We should try to reduce charges on atoms if it is a possible. Now, we are going to reduce charges on drawn structure.
You see charges of atoms are reduced. Now, there are no charges in atoms. therefore, this structure should be a the lewis structure of phosphorous acid.