AsF6- Lewis Structure,Geometry:13 Facts You Should Know


This article aims at explaining the Asf6- lewis structure, geometry, and other important concepts of arsenic hexafluoride. AsF6 has an octahedral geometry. The central atom arsenic is sp3d2 hydridized, and all six fluorine atoms form a 90and 180 bond angles in an octahedral geometry.

How to draw Asf6- lewis structure?

In order to draw the AsF6- lewis structure, we  assign a central molecule, count the number of valence electrons of each atom present in the molecule and satisfy the octet of all atoms. This is how we draw the lewis structure of a molecule.

In AsF6 arsenic is the central atom as it is the least electronegative(also least in number in this case); it is  also the only atom that forms more than one bond.

Arsenic belongs to group 15 and has five valence electrons(4s24p3), and fluorine belongs to group 17 and has seven valence electrons(2s22p5). There are six fluorine atoms present along with a negative charge. The total number of valence electrons present=5+7*(6) +1=48.

Each fluorine atom forms a single bond with arsenic and adopts an octahedral geometry. We will draw the lone pairs on fluorine as dots. The lewis structure of AsF6is shown below:

Asf6- lewis structure octet rule

Atoms that show covalent bonding try to have eight electrons in their valence shell. This is the octet rule. It explains chemical bonding in a lot of cases ;however there are many exceptions to this rule.

Arsenic has five valence electrons and would need three more to complete its valence shell. However, it does not obey the octet rule and has an expanded octet with twelve valence electrons(five of arsenic, one electron from the negative charge, and six electrons from the fluorine atoms). It utilizes its d-orbital to expand its octet.

Fluorine has seven valence electrons in its shell. It needs one more to complete its octet, which it does by forming a covalent bond with arsenic(six non-bonding electrons and two bonding electrons).

AsF6 lewis structure lone pairs

AsF6 has forth eight valence electrons, out of which twelve are bonding electrons, and the remaining thirty-six are non-bonding electrons present on six fluorine atom. The twelve bonding electrons are distributed between the six arsenic and fluorine covalent bonds. Six non-bonding electrons or three lone pairs are present on each fluorine atoms.

AsF6- lewis structure formal charge

The given formula can calculate the formal charge on each atom:

Formal charge= (Valence electrons on free atom)-1/2(total number of shared electrons) – (total number of unshared electrons)

We will calculate the formal charge on arsenic and fluorine.

Valence electrons on free As= 5

Total number of shared electrons= 12

Total number of unshared electrons= 0

Formal charge of As in AsF6- = 5-1/2(12)-0= -1

Valence electrons on free fluorine atom= 7

Total number of shared electrons= 2

Total number of unshared electrons= 6

Formal charge of F in AsF6 = 7 – 1/2 (2) – 6 =0

The As atom and fluorine atom in Asf6- lewis structure have -1 and 0 formal charges, respectively.

AsF6 lewis structure resonance

We can draw resonating structures of a molecule only if it has double or triple bonds along with lone pairs present on the atoms, which leads to the delocalization of electrons. In such cases, we can draw multiple lewis structures for a given molecule known as resonance. In the case of AsF6,  no multiple bonds are present; therefore, only one lewis structure is possible(no resonance).

Asf6- lewis structure shape

According to VSEPR theory, the central atom is As, which forms covalent bonds with six fluorine atoms, with the molecular and electron geometry being octahedral.

The six fluorine atoms are symmetrically arranged around the central atom arsenic along the vertices of an octahedron. Here all the atoms around the central atom are the same, so a regular octahedral geometry is formed(when different atoms surround the central atom, in this case, there can be a distortion in geometry, also known as the Jahn-Teller effect).

According to VSEPR theory, the electron density(bond pairs, lone pairs, and electrons of multiple bonds) is arranged to minimize repulsions by being as far apart as possible. The shape of an AX6 type molecule with six bonded atoms and zero lone pairs is octahedral.

AsF6 shape

Asf6- lewis structure angle

There is no lone pair present on the central atom, and therefore the bond angles are 90. The central atom, arsenic, is bonded to six fluorine atoms in an octahedral geometry with sp3d2 hybridization.

Asf6- valence electrons

In AsF6- lewis structure, arsenic has five valence electrons(4s24p3) and each fluorine atom has seven valence electrons(2s22p5). The total valence electrons in AsF6- lewis structure are 5+7*6 =48.

Asf6- hybridization

AsF6 has an octahedral geometry. Arsenic uses 4s, three 4p orbitals, and two 4d orbitals to form six sp3d2 hybrid orbitals. Hybridization is a theoretical concept in which atomic orbitals undergo mixing to form hybrid orbitals which have lower energy than the atomic orbitals and have a definite direction in space.

Is Asf6- acidic or basic?

Arsenic hexafluoride ion might accept electrons as it has vacant 4d orbitals and acts as a lewis acid. The oxidation state of arsenic in AsF6 is +5, which is one of the stable oxidation states of arsenic(-3, +3, and +5 are stable oxidation states of arsenic). Therefore AsF6is stable and will not donate electrons or act as a Lewis base.

Is Asf6- ionic?

AsF6 is an anion and negatively charged(-1) so yes, it is ionic. It can form a stable salt when combined with Caesium, Rubidium, lithium, sodium, etc.

Is Asf6- polar or non-polar?

AsF6- forms an octahedral geometry in which all the dipole moment of As-F bonds gets canceled as they are in opposite directions and of equal intensity due to bonds between the same atoms(As-F). Therefore, AsF6 is non-polar due to its molecular geometry despite having polar As-F bonds.

Asf6- solubility

AsF6ion, when present in Lithium hexafluoroarsenate i.e., AsF6Li or AsF6Na, is soluble in water.

Conclusion

In this article, we studied the lewis structure of arsenic hexafluoride anion, its shape, hybridization, polarity, lone pairs, etc.

Sakshi Anand

Hello, I am Sakshi Anand and I am here to make chemistry easy and enjoyable to read. Complex ideas do not require complex language. I am an avid reader and enjoy researching intensively.

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