AsCl5 Lewis structure

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AsCl5 Lewis Structure
AsCl5 Lewis structure

AsCl5 (arsenic pentachloride) has one arsenic atom and five chlorine atoms.

In AsCl5 Lewis structure, there are five single bonds around the arsenic atom, with five chlorine atoms attached to it, and on each chlorine atom, there are three lone pairs.


Use these steps to correctly draw the AsCl5 Lewis structure:

#1 First draw a rough sketch
#2 Mark lone pairs on the atoms
#3 Calculate and mark formal charges on the atoms, if required

Let’s discuss each step in more detail.

#1 First draw a rough sketch

  • First, determine the total number of valence electrons
Periodic table

In the periodic table, arsenic lies in group 15, and chlorine lies in group 17.

Hence, arsenic has five valence electrons and chlorine has seven valence electrons.

Since AsCl5 has one arsenic atom and five chlorine atoms, so…

Valence electrons of one arsenic atom = 5 × 1 = 5
Valence electrons of five chlorine atoms = 7 × 5 = 35

And the total valence electrons = 5 + 35 = 40

  • Second, find the total electron pairs

We have a total of 40 valence electrons. And when we divide this value by two, we get the value of total electron pairs.

Total electron pairs = total valence electrons ÷ 2

So the total electron pairs = 40 ÷ 2 = 20

  • Third, determine the central atom

We have to place the least electronegative atom at the center.

Since arsenic is less electronegative than chlorine, assume that the central atom is arsenic.

Therefore, place arsenic in the center and chlorines on either side.

  • And finally, draw the rough sketch
AsCl5 Lewis Structure (Step 1)
Rough sketch of AsCl5 Lewis structure

#2 Mark lone pairs on the atoms

Here, we have a total of 20 electron pairs. And five As — Cl bonds are already marked. So we have to only mark the remaining fifteen electron pairs as lone pairs on the sketch.

Also remember that arsenic is a period 4 element, so it can keep more than 8 electrons in its last shell. And chlorine is a period 3 element, so it can keep more than 8 electrons in its last shell.

Always start to mark the lone pairs from outside atoms. Here, the outside atoms are chlorines.

So for each chlorine, there are three lone pairs, and for arsenic, there is zero lone pair because all fifteen electron pairs are over.

Mark the lone pairs on the sketch as follows:

AsCl5 Lewis Structure (Step 2)
Lone pairs marked, and got the stable Lewis structure of AsCl5

#3 Calculate and mark formal charges on the atoms, if required

Use the following formula to calculate the formal charges on atoms:

Formal charge = valence electrons – nonbonding electrons – ½ bonding electrons

For arsenic atom, formal charge = 5 – 0 – ½ (10) = 0

For each chlorine atom, formal charge = 7 – 6 – ½ (2) = 0

Here, both arsenic and chlorine atoms do not have charges, so no need to mark the charges.

In the above structure, you can see that the central atom (arsenic) forms an octet. And the outside atoms (chlorines) also form an octet. Hence, the octet rule is satisfied.

Therefore, this structure is the stable Lewis structure of AsCl5.

Next: COBr2 Lewis structure

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