In the lewis structure of P2O5, there are two elements; phosphorus and oxygen. Two phosphorus atoms are linked through an oxygen atom in the lewis structure of phosphorus pentoxide (P2O5). All other oxygen atoms have made double bonds with phosphorus atoms. Steps of the drawing lewis structure of P2O5 molecule are explained in detail in this tutorial.
In this lewis structure, center oxygen atom has made single bonds with two phosphorus atoms. Each phosphorus atom has made bonds with three oxygen atoms. There are four (P=O) double bonds in this molecule. Also, there are no charges on atoms in P2O5 lewis structure.
When you are trying to draw a lewis structure, there are guidelines to do it. 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.
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.
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, P2O5, Total pairs of electrons are twenty in their valence shells.
To be the center atom in a molecule, ability of having greater valance is important. Then, from oxygen and phosphorus atoms, which atom has the highest valence? 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 P2O5. But, there are two phosphorus atoms. So, we can draw the sketch of P2O5.
After determining the center atom and sketch of P2O5 molecule, we can start to mark lone pairs on atoms. Remember that, there are total of twenty electron pairs to mark as bonds and lone pairs.
There are charges on each atom. 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 +2 charge.
When there are charges on lot of atoms in a drawn sketch, it is not stable. That means, when there are least charges on atoms, that structure is very much stable. Because, there are charges on most atoms in our current P2O5 structure, that structure is very unstable. Therefore, we can reduce charges of atoms by converting lone pairs to bonds step by step. Those steps are figured below.
You can see, in our final structure, there are no charges on any atom. That means, that is the most stable structure and it is the lewis structure of P2O5 .