P2O3 (Phosphorus trioxide) Lewis Structure
In the lewis structure of P2O3, (Phosphorus trioxide), there are two elements; phosphorus and oxygen. Two phosphorus atoms are linked through the center oxygen atom in the lewis structure of phosphorus pentoxide (P2O5). Other two oxygen atoms have made double bonds with phosphorus atoms. Steps of the drawing lewis structure of P2O3 molecule are explained in detail in this tutorial. So, you can learn how to properly draw a lewis structure.
P2O3 lewis structure
In this P2O3 lewis structure, center oxygen atom has made single bonds with two phosphorus atoms. Each phosphorus atom has made a double bond with a oxygen atoms. There are two (P=O) double bonds in this lewis structure. Also, there are no charges on atoms in P2O3 lewis structure.
Steps of drawing lewis structure of P2O3 lewis structure
There are guidelines to do draw a lewis structure properly. Number of steps can be changed according the complexity of the molecule or ion. Because P2O5 molecule is bit complex molecule, (if you are beginner to lewis structure drawing) you have to be careful when it starts to draw.
- Find total number of electrons of the valance shells of phosphorus and oxygen atom
- Total electrons pairs existing as lone pairs and bonds
- Center atom selection
- Mark lone pairs on atoms
- Mark charges on atoms if there are charges
- Check the stability and minimize charges on atoms by converting lone pairs to bonds to obtain best lewis structure.
Total number of electrons of the valance shells of P2O3
There are only two elements in phosphorus pentoxide; phosphorus and oxygen. Phosphorus is a group VA element in the periodic table and has five electrons in its last shell (valence shell). Oxygen is a group VIA element in the periodic table and contains six electrons in its last shell. When calculating total valence electrons given by atoms, you should multiply the valence electrons of an element by number of respective element. Study how it is done below.
- valence electrons given by phosphorus atoms = 5 * 2 = 10
- valence electrons given by oxygen atoms = 6 * 3 = 18
- Total valence electrons = 10 + 18 = 28
Total valence electrons pairs
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, P2O3, Total pairs of electrons are fourteen in their valence shells.
Selection of center atom of P2O3
Selection of center atom is important to decide the structure of the molecule. Other atoms are located around the center atom. To be the center atom in a molecule, ability of having greater valance is important. Then, from oxygen and phosphorus atoms, we should identify the center atom. We know, it is phosphorus. Maximum valence of phosphorus is five. Oxygen's only valence is two. Therefore, phosphorus atom should be the center atom of P2O3. But, there are two phosphorus atoms. So, we can draw the sketch of P2O3 as below.
Mark lone pairs on atoms of P2O3
After determining the center atom and sketch of P2O3, we can start to mark lone pairs on atoms. Remember that, there are total of fourteen electron pairs to mark as bonds and lone pairs.
- There are already four sigma bonds in the drawn sketch (four P-O bonds). Now only ten (14-4=10) lone pairs are remaining to mark on atoms.
- Usually, those remaining electron pairs should be started to mark on outside atoms. Then, mark lone pairs on oxygen atoms protecting the octal rule. Each outside oxygen atom will take three lone pairs. Now, six electron pairs were marked as lone pairs on outside oxygen atoms. So, now there are four lone pairs to mark on center oxygen atom and phosphorus atoms. Mark two lone pairs on center oxygen atom. Then each phosphorus atom will get one lone pair.
- Now, marking of lone pairs on atoms is done.
Mark charges on atoms
There are charges on some atoms. Marking those charges is important to obtain the best lewis structure (most stable). Each outside oxygen atom has -1 charge and each phosphorus atom has +1 charge.
Check the stability and minimize charges on atoms by converting lone pairs to bonds
When there are charges on lot of atoms in a drawn sketch, that structure is not stable. That means, when there are least charges on atoms, that structure is very much stable. Because, there are charges on some atoms in our current P2O3 structure, that structure is not unstable. Therefore, we can reduce charges of atoms by converting lone pairs to bonds step by step. Those steps are explained in the following figure.
You can see, in our final structure, there are no charges on any atom. That means, that is the most stable structure we can draw and it is the lewis structure of P2O3 .
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