So you have seen the above image by now, right?
Let me explain the above image in short.
AsH3 lewis structure has an Arsenic atom (As) at the center which is surrounded by three Hydrogen atoms (H). There are 3 single bonds between the Arsenic atom (As) and each Hydrogen atom (H). There is 1 lone pair on the Arsenic atom (As).
If you haven’t understood anything from the above image of AsH3 lewis structure, then just stick with me and you will get the detailed step by step explanation on drawing a lewis structure of AsH3.
So let’s move to the steps of drawing the lewis structure of AsH3.
Steps of drawing AsH3 lewis structure
Step 1: Find the total valence electrons in AsH3 molecule
In order to find the total valence electrons in AsH3 molecule, first of all you should know the valence electrons present in arsenic atom as well as hydrogen atom.
(Valence electrons are the electrons that are present in the outermost orbit of any atom.)
Here, I’ll tell you how you can easily find the valence electrons of arsenic as well as hydrogen using a periodic table.
Total valence electrons in AsH3 molecule
→ Valence electrons given by arsenic atom:
Arsenic is a group 15 element on the periodic table.  Hence the valence electrons present in arsenic is 5.
You can see the 5 valence electrons present in the arsenic atom as shown in the above image.
→ Valence electrons given by hydrogen atom:
Hydrogen is group 1 element on the periodic table.  Hence the valence electron present in hydrogen is 1.
You can see that only 1 valence electron is present in the hydrogen atom as shown in the above image.
Total valence electrons in AsH3 molecule = valence electrons given by 1 arsenic atom + valence electrons given by 3 hydrogen atoms = 5 + 1(3) = 8.
Step 2: Select the central atom
For selecting the center atom, you have to remember that the atom which is less electronegative remains at the center.
(Remember: If hydrogen is present in the given molecule, then always put hydrogen outside.)
Now here the given molecule is AsH3 and it contains arsenic atom (As) and hydrogen atoms (H).
You can see the electronegativity values of arsenic atom (As) and hydrogen atom (H) in the above periodic table.
If we compare the electronegativity values of arsenic (As) and hydrogen (H) then the hydrogen atom is less electronegative. But as per the rule we have to keep hydrogen outside.
So here the arsenic atom (As) is the center atom and the hydrogen atoms (H) are the outside atoms.
Step 3: Connect each atoms by putting an electron pair between them
Now in the AsH3 molecule, you have to put the electron pairs between the arsenic atom (As) and hydrogen atoms (H).
This indicates that the arsenic (As) and hydrogen (H) are chemically bonded with each other in a AsH3 molecule.
Step 4: Make the outer atoms stable. Place the remaining valence electrons pair on the central atom.
Now in this step, you have to check the stability of the outer atoms.
Here in the sketch of AsH3 molecule, you can see that the outer atoms are hydrogen atoms.
These outer hydrogen atoms are forming a duplet and hence they are stable.
Also, in step 1 we have calculated the total number of valence electrons present in the AsH3 molecule.
The AsH3 molecule has a total 8 valence electrons and out of these, only 6 valence electrons are used in the above sketch.
So the number of electrons which are left = 8 – 6 = 2.
You have to put these 2 electrons on the central arsenic atom in the above sketch of AsH3 molecule.
Now let’s proceed to the next step.
Step 5: Check the octet on the central atom
In this step, you have to check whether the central arsenic atom (As) is stable or not.
In order to check the stability of the central arsenic (As) atom, we have to check whether it is forming an octet or not.
You can see from the above picture that the arsenic atom is forming an octet. That means it has 8 electrons.
And hence the central arsenic atom is stable.
Now let’s proceed to the final step to check whether the lewis structure of AsH3 is stable or not.
Step 6: Check the stability of lewis structure
Now you have come to the final step in which you have to check the stability of lewis structure of AsH3.
The stability of lewis structure can be checked by using a concept of formal charge.
In short, now you have to find the formal charge on arsenic (As) atom as well as hydrogen (H) atoms present in the AsH3 molecule.
For calculating the formal charge, you have to use the following formula;
Formal charge = Valence electrons – (Bonding electrons)/2 – Nonbonding electrons
For Arsenic (As) atom:
Valence electrons = 5 (because arsenic is in group 15)
Bonding electrons = 6
Nonbonding electrons = 2
For Hydrogen (H) atom:
Valence electron = 1 (because hydrogen is in group 1)
Bonding electrons = 2
Nonbonding electrons = 0
From the above calculations of formal charge, you can see that the arsenic (As) atom as well as hydrogen (H) atom has a “zero” formal charge.
This indicates that the above lewis structure of AsH3 is stable and there is no further change in the above structure of AsH3.
In the above lewis dot structure of AsH3, you can also represent each bonding electron pair (:) as a single bond (|). By doing so, you will get the following lewis structure of AsH3.
I hope you have completely understood all the above steps.
For more practice and better understanding, you can try other lewis structures listed below.
Try (or at least See) these lewis structures for better understanding:
|AsF3 Lewis Structure
|KrF2 Lewis Structure
|SO2Cl2 Lewis Structure
|C4H10 (Butane) Lewis Structure
|C2H3Cl Lewis Structure
|CH2Br2 Lewis Structure
Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. He is a founder of Pediabay and is passionate about helping students through his easily digestible explanations.
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