AsF5 Lewis structure

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AsF5 Lewis Structure
AsF5 Lewis structure

AsF5 (arsenic pentafluoride) has one arsenic atom and five fluorine atoms.

In AsF5 Lewis structure, there are five single bonds around the arsenic atom, with five fluorine atoms attached to it, and on each fluorine atom, there are three lone pairs.


Use these steps to correctly draw the AsF5 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 fluorine lies in group 17.

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

Since AsF5 has one arsenic atom and five fluorine atoms, so…

Valence electrons of one arsenic atom = 5 × 1 = 5
Valence electrons of five fluorine 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 fluorine, assume that the central atom is arsenic.

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

  • And finally, draw the rough sketch
AsF5 Lewis Structure (Step 1)
Rough sketch of AsF5 Lewis structure

#2 Mark lone pairs on the atoms

Here, we have a total of 20 electron pairs. And five As — F 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 fluorine is a period 2 element, so it can not keep more than 8 electrons in its last shell.

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

So for each fluorine, 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:

AsF5 Lewis Structure (Step 2)
Lone pairs marked, and got the stable Lewis structure of AsF5

#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 fluorine atom, formal charge = 7 – 6 – ½ (2) = 0

Here, both arsenic and fluorine 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 (fluorines) also form an octet. Hence, the octet rule is satisfied.

Therefore, this structure is the stable Lewis structure of AsF5.


What are the valence electrons for AsF5?

AsF5 has one arsenic atom and five fluorine atoms.

The valence electrons for AsF5 can be determined by adding the valence electrons of the constituent atoms.

Arsenic has 5 valence electrons, and each fluorine atom has 7 valence electrons. Therefore, AsF5 has a total of 5(1) + 7(5) = 40 valence electrons.

Does AsF5 satisfy the octet rule?

In AsF5 Lewis structure, arsenic has 10 electrons (expanded octet) and each fluorine has 8 electrons.

Now arsenic is a period 4 element, meaning that it can hold more than 8 electrons in its last shell, so an expanded octet of the arsenic atom is okay.

Hence, both arsenic and fluorine satisfy the octet rule in AsF5 Lewis structure.

How many lone pairs does arsenic have in AsF5?

In AsF5 Lewis structure, the central atom (arsenic) is surrounded by five fluorine atoms, and each fluorine atom makes a single bond with the arsenic atom.

Remember that while drawing Lewis structures, the lone pairs are always marked on the outside atoms first and then, on the central atom.

So, each fluorine in AsF5 has three lone pairs and the central atom (arsenic) has zero lone pair.

Next: HI Lewis structure

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