Phosphorus oxychloride (POCl3) Lewis structure
Phosphorus oxychloride (POCl3) lewis structure contains one phosphorus atom, one oxygen atoms and and three chlorine atoms. The oxygen atom has made a double bond with phosphorus atom. Each chlorine atom has made single bonds with center phosphorus atom. In this tutorial, we will learn how to draw POCl3O lewis structure.
POCl3O lewis structure
We will see what are the characteristics of POCl3 lewis structure.
- Only oxygen atom has made a double bond with phosphorus atom. Also, that oxygen atom has two lone pairs on its last shell.
- As well as, each chlorine atom has made a single bond with an phosphorus atom. Each chlorine atom has three lone pairs in valence shell.
- Phosphorus atom, the center atom has five bonds around it.
Steps of drawing lewis structure of POCl3
When we draw a lewis structure of a molecule or an ion, there are specific guidelines and steps. Number of steps you need to draw the lewis structure, can be changed according the complexity of the molecule or ion. Those all steps and guidelines are mentioned and explained in detail in this tutorial for your knowledge improvement.
- Find total number of electrons of the valance shells of phosphorus, chlorine and oxygen atoms
- Find total number of electrons pairs existing as lone pairs and bonds
- Determine center atom
- Mark lone pairs on atoms
- Mark charges on atoms if there are.
- Check the stability and minimize charges on atoms by converting lone pairs to bonds to obtain best lewis structure.
Find total number of electrons of the valance shells of POCl3
There are three elements in POCl3 molecule. To determine number of electrons in valence shell of atom, you need to know that where (respective group) an element is located in the periodic table.
- Oxygen, a VIA group element has six electrons in its last shell.
- Phosphorus is a group VA element in the periodic table and contains five electrons in its last shell.
- Chlorine is located at VIIA group and has seven electrons in its valence shell.
Now, we know how many electrons are there in valence shells of oxygen, phosphorus and chlorine atoms. To find out total number of valence electrons given by an specific element in a molecule, you should multiply number of valence electrons by number of respective atoms in that molecule as below.
- valence electrons given by oxygen atoms = 6 * 1 = 6
- valence electrons given by phosphorus atom = 5 * 1 = 5
- valence electrons given by chlorine atom = 7 * 3 = 21
- Because, there is no overall charge in molecule, no additions or deductions to total number of valence electrons.
- Total number of valence electrons = 6 + 5 + 21
- Total number of valence electrons = 32
Determine 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, phosphorus oxychloride, total number of pairs of electrons are sixteen in their valence shells.
Selection of center atom of POCl3
Deciding the center atom is an important step in drawing the lewis structure. Having higher valence and being the most electropositive element are the key facts of selection of center atom.
- Fact 1: Because, chlorine atom can show higher valence (7) than oxygen atom (2) and phosphorus atom (5), chlorine atom has the higher priority to be the center atom.
- Fact 2: But, phosphorus is more electropositive than oxygen and chlorine, phosphorus atom should be the center atom.
- From above two facts, it can be decided that phosphorus or chlorine should be the center atom in POCl3.
- Now, there is a confusion of selecting the center atom.
- Fact 3: Considering the stability of phosphorus and chlorine atoms when they make covalent compounds, there should be at least three bonds around phosphorus atom because phosphorus has only two valences (3, 5). But for chlorine, it is enough to have one bond because chlorine has variety of valences (1, 3, 5, 7)
- From fact 3, we can decide that, phosphorus atom should be the center atom because there should be at least three bonds around phosphorus atom.
- By thinking like this, we have found that following skeletal is the most suitable one to draw the most stable lewis structure of phosphorus oxychloride.
Mark lone pairs on atoms
After determining the center atom and skeletal of POCl3 molecule, we can start to mark lone pairs on atoms. Remember that, there are total of sixteen electron pairs to mark as lone pairs and bonds.
- There are already four bonds in the above drawn skeletal. So, there are twelve remaining lone pairs to mark on atoms.
- Start to mark remaining lone pairs on outside atoms (in this case: oxygen and chlorine atoms). Oxygen atom will take three lone pairs. Now, nine more lone pairs are remaining.
- Then, you can mark remaining lone pairs on chlorine atoms. Each chlorine atom will take three lone pairs and all remaining nine lone pairs are on three chlorine atoms.
Mark charges on atoms
There are charges above drawn structure as below (Oxygen atom has -1 charge and phosphorus atom has +1 charge).
Check the stability and minimize charges on atoms by converting lone pairs to bonds
There are charges on two atoms in above structure. If we can reduce charges furthermore by converting lone pairs to bonds to get more stable structure, try that step.
Therefore, convert a lone pair on oxygen atom to form a double bond between that oxygen atom and center phosphorus atom as following image. Then, charges of phosphorus and oxygen atoms will be zero.
Then, there are no charges furthermore in new structure we can consider this is the lewis structure of POCl3.
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