Arsenic pentafluoride (AsF5) lewis dot structure, molecular geometry, hybridization, polar or nonpolar

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AsF5 lewis structure molecular geometry

Arsenic pentafluoride is a chemical compound made up of arsenic and fluorine. It is also called pnictogen halide. It appears as a colorless gas and soluble in Ethanol, Dimethyl ether, Benzene.

In this article, we will discuss Arsenic pentafluoride (AsF5) lewis structure, molecular geometry, hybridization, polar or nonpolar, its bond angle, etc.

Arsenic pentafluoride is a dangerous toxin and it smells similar to vinyl chloride gas.

Name of MoleculeArsenic pentafluoride
Chemical formulaAsF5
Molecular geometry of AsF5Trigonal bipyramidal
Electron geometry of AsF5Trigonal bipyramidal
HybridizationSp3d
NatureNonpolar molecule
Bond angle90° / 120°
Total Valence electron for AsF540

How to draw lewis structure of AsF5?

AsF5 lewis structure is made up of one Arsenic atom situated in a central position and five fluorine atoms that spaced evenly around the central atom. There is a total of 10 bonding electrons and 30 nonbonding electrons present in the lewis structure of AsF5.

The lewis structure of AsF5 violates the octet rule as its central atom holds more than 8 electrons. Let’s see how to draw this in a simple way.

Follow some steps for drawing the lewis dot structure for AsF5

1. Count total valence electron in AsF5

First of all, determine the valence electron that is available for drawing the lewis structure of AsF5 because the lewis diagram is all about the representation of valence electrons on atoms.

So, an easy way to find the valence electron of atoms in the AsF5 molecule is, just to look at the periodic group of arsenic and fluorine atoms.

As arsenic atom belongs to group 15th in periodic table and fluorine situated in 17th group, hence, the valence electron for arsenic is 5 and for fluorine atom, it is 7.

⇒ Total number of the valence electrons in arsenic = 5

⇒ Total number of the valence electrons in fluorine = 7

∴ Total number of valence electron available for the AsF5 Lewis structure = 5 + 7(5) = 40 valence electrons         [∴AsF5 molecule has one arsenic and five fluorine atoms]

Total number of valence electron available for the AsF5 Lewis structure

2. Find the least electronegative atom and place it at center

An atom with a less electronegative value is more preferable for the central position in the lewis diagram because they are more prone to share the electrons with surrounding atoms.

In the case of the AsF5 molecule, the arsenic atom is less electronegative than the fluorine atom, also, fluorine is the highest electronegative element in chemistry, hence, it always takes the surrounding position in the lewis diagram.

So, just put the arsenic in the center position and spread all fluorine atoms around it.

central position in AsF5 lewis structure

3. Connect outer atoms to central atom with a single bond

In this step, place the single bond in between the outer atom(fluorine) and central atoms(arsenic).

Connect outer atom to central atom in AsF5 molecule

After connecting each outer atom to the central atom, count the number of valence electrons used in the above structure. There are 5 single used in the above structure, and one single bond means 2 electrons.

Hence, in the above structure, (2 × 5) = 10 valence electrons are used from a total of 40 valence electrons available for drawing the AsF5 Lewis structure.

∴ (40 – 10) = 30 valence electrons

So, we are left with 30 valence electrons more.

4. Place remaining electrons on outer atoms and complete their octet

Let’s start putting the remaining valence electrons on outer atoms first to complete the octet i.e. Each atom should contain 8 electrons to complete the octet, an exception may occur. 

In the AsF5 molecule, fluorine is the outer atom and it needs 8 electrons in its valence shell to complete the octet.

AsF5 lewis structure

So, all fluorine atoms in the above structure completed their octet, because all of them have 8 electrons(6 electrons represented as dots + 2 electrons in every single bond) in their valence shell. 

Also, the central atom Arsenic has 10 electrons(5 single bonds) in its valence shell.

The central atom Arsenic has expanded octet that means it can hold more than 8 electrons in its valence shell.

Arsenic atom has d-orbital to accommodate additional electrons.

Now again count the total valence electrons used in the above structure.

In the above structure, there are 30 electrons represented as dots + 5 single bonds means 10 electrons are used.

Hence, (30 + 10) = 40 total electrons are used in the above structure and we had a total of 40 valence electrons available for the AsF5 lewis structure.

Now just check the formal charge for the above AsF5 lewis structure.

5. Check the stability with the help of a formal charge concept

The lesser the formal charge on atoms, the better is the stability of the lewis diagram.

To calculate the formal charge on an atom. Use the formula given below-

⇒ Formal charge = (valence electrons – lone pair electrons –  1/2 bonding electrons)

Let’s count the formal charge on the fluorine atom first, all fluorine atoms in the AsF5 Lewis structure(4th step) have the same bonded pair and lone pair, so, just count the F.C. for the one fluorine atom.

For fluorine atom:

⇒ Valence electrons of fluorine = 7

⇒ Lone pair electrons on fluorine = 6

⇒ Bonding electrons around fluorine(1 single bond) = 2

∴ (7 – 6 – 2/2) = 0 formal charge on all fluorine atoms.

 For arsenic atom

⇒ Valence electrons of arsenic = 5

⇒ Lone pair electrons on arsenic = 0

⇒ Bonding electrons around arsenic (5 single bonds) = 10

∴ (5 – 0 – 10/2) = 0 formal charge on the arsenic central atom.

formal charge in AsF5 lewis structure

AsF5 lewis structure

So, all the atoms in the AsF5 Lewis structure have a formal charge equal to zero. Therefore, the above lewis structure of Arsenic pentafluoride is most appropriate and stable.

What are the electron and molecular geometry of AsF5?

The molecular geometry of AsF5 is Trigonal bipyramidal because the central atom arsenic is surrounded by five regions of electron density and all the regions are bonding regions, as per VSEPR theory, the repulsion between these 5 bonding regions is maximum when they afford a geometry called trigonal bipyramidal.

The arsenic central atom in AsF5 molecular shape shares a plane with three fluorine atoms in equatorial position and two more fluorine atoms in axial position.

AsF5 molecular geometry or shape

AsF5 molecular geometry

Since there is no lone pair present on the central atom in the AsF5 molecule, its electron geometry will be the same as its molecular geometry which is trigonal bipyramidal.

Hybridization of AsF5

Let’s find the hybridization of AsF5 through the steric number of its central atom.

“Steric number is the addition of a total number of bonded atoms around a central atom and the lone pair present on it.”

∴ Steric number of AsF5 = (Number of bonded atoms attached to arsenic + Lone pair on arsenic)

As per the lewis structure of AsF5, the arsenic atom is bonded with five fluorine atoms and it contains no lone pair of electrons.

∴ Steric number of AsF5 = (5 + 0) = 5

Steric numberHybridization
1S
2Sp
3Sp²
4Sp³
5Sp³d
6Sp³d²

So, for a steric number of five, we get the Sp3d hybridization on the arsenic atom in the AsF5 molecule.

The bond angle of AsF5

Since AsF5 forms trigonal bipyramidal geometry, it will have two bond angles, 120º and 90º.

In AsF5, the three fluorine atoms are in the same plane at 120° angles to each other in equatorial positions, and two more fluorine atoms that are in the axial position form a 90° bond angle.

Arsenic pentafluoride polarity: is AsF5 polar or nonpolar?

Is AsF5 polar or non-polar? AsF5 is a nonpolar molecule because it forms the trigonal bipyramidal geometry which is symmetrical, hence, all dipoles that are generated along with the five bonds(As-F) will cancel out easily, giving the molecule zero net dipole moment.

Although the bonds(As-F) are polar in nature because of electronegativity difference according to the Pauling scale. But due to the highly symmetrical structure of AsF5, all polarity gets canceled out, giving net polarity of AsF5 zero.

FAQ

How many shared electrons and unshared electrons are present in the lewis structure of AsF5?

Shared electrons are those that are present in between the two atoms, they help to make the covalent bonds between the atoms, and they are also called bonding electrons.

Unshared electrons are basically lone pair electrons that do not take part in the formation of bonds between atoms.

Now, in the AsF5 lewis structure, the number of shared electrons is 10(5 single bonds) and the number of unshared electrons is 30(represented as dots).

Why does the AsF5 lewis structure violate the octet rule?

If we see the lewis structure of AsF5, we observe that all fluorine atom gets 8 electrons in their valence shell, hence, follow the octet rule. But the central atom Arsenic is connected to 5 single bonds means 10 electrons.

So, here, the arsenic atom in the AsF5 lewis structure has 10 valence electrons in its valence shell which obviously violates the octet.

Now the arsenic atom violates the octet because it has the ability to expand the octet and holds more than 8 electrons by accommodating extra electrons via the d-orbital.

Some central atom can expand their octet for reducing the formal charge on the lewis diagram or attaining stability by storing extra electrons needed for bonding.

Properties of Arsenic pentafluoride

  • It has a molar mass of 169.9136 g mol−1.
  • It is a highly toxic colorless gas.
  • It has a boiling point of −52.8 ˚C and a melting point of −79.8 ˚C.
  • Its oxidation state is +5.

Reactions of Arsenic pentafluoride

Arsenic pentafluoride reacts with sulfur tetrafluoride to form an ionic complex.

⇒ AsF5 + SF4 → SF3+ + AsF6

Arsenic pentafluoride is prepared by a simple combination of fluorine and arsenic.

⇒ 2As + 5F2 → 2AsF5

When arsenic trifluoride reacts with fluorine, it forms arsenic pentafluoride.

⇒ AsF3 + F2 → AsF5

When two moles of arsenic pentoxide or arsenic trioxide react with 10 moles of fluorine, it forms arsenic pentafluoride.

⇒ 2As2O5 + 10F2 → 4AsF5 + 5O2

⇒ 2As2O3 + 10F2 → 4AsF5 + 3O2

Summary

  • The total valence electron is available for drawing the AsF5 Lewis structure is 40.
  • The molecular geometry of AsF5 is trigonal bipyramidal and its electron geometry is also the same.
  • The lewis structure of AsF5 has 5 bonding pairs and 15 nonbonding pairs.
  • AsF5 is a nonpolar molecule because of symmetrical geometry that makes the net dipole moment zero.
  • The hybridization of AsF5 is Sp3d as its central atom steric number is 5.
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