AsF3 Lewis Structure, Geometry: 13 Facts You Should Know


In this article, “asf3 lewis structure”, structure, geometry. Acidic or basic properties, formal charge calculation with detailed explanations are discussed below.

Arsenic trifluoride is mainly a gaseous compound but it is also found in solid state also. It is pyramidal structured with bond angle (F-As-F) 96.20 and As-F bond length is 170.6 pm. Arsenic is sp3 hybridized in AsF3 molecule in which three bond pairs and one lone pair are present.

Let’s focus on the following topics on arsenic trifluoride.

How to draw AsF3 lewis structure?

To know the process of drawing a lewis structure, first you have to know what is lewis structure. It is basically a structural representation of a molecule where the nonbonding electrons are shown around the respective participating atoms in the lewis structure.

  1. Determination of valance electron: In this molecule, AsF3, central atom, arsenic and substituent atoms fluorine have three and five electrons respectively in their outer most shell.
  2. Finding out the bonding electrons: Total three covalent bonds are present in this molecular species. Thus (3×2 = 6) electrons are involved in bonding.
  3. Finding out the nonbonding electrons:  Arsenic has two nonbonding electrons and fluorine has total five electrons as nonbonded.

AsF3 Lewis Structure Shape

Shape and structure of any molecule is almost two similar words only if there is no repulsion involving bond pair and lone pair is present. Geometrical structure only depends upon the hybridization of central atom but shape of any molecule depends upon the following parameters-

  1. Hybridization
  2. Repulsion involving lone pair and bond pairs.

Repulsion between bond pair and lone pair can be three types-

  • Lone pair- lone pair repulsion
  • bond pair-bond pair repulsion
  • lone pair-bond pair repulsion

The increasing order of the above repulsive factor is-

bond pair -bond pair repulsion < Lone pair – bond pair repulsion < Lone pair- lone pair repulsion.

In AsF3, arsenic and fluorine have five and seven electrons in their respective valance shell or outer most shell. The valance shell electron configuration of As and F are 2s2 2p3 and 2s2 2p5. Among these five electrons of arsenic, three electrons participate in covalent bond formation with three fluorine atoms. Rest of the two valance electrons remain as nonbonded.

These two lone electrons face repulsion from the bonding electrons. As there is only one lone pair, lone pair-lone pair repulsion is insignificant for this molecule.

 For this bond pair-bond pair repulsion and lone pair – bond pair repulsion, this molecule is deviated from its actual geometrical structure (tetrahedral) and shows a trigonal pyramidal structure with three bond pairs and one lone pair on central atom, arsenic.

AsF3 Lewis Structure Formal Charge

The calculation of formal charge of each of the atom in a molecule is very much significant in chemistry because it helps to detect the most stable lewis structure. The structural representation having maximum number of zero formal charge of its respective atoms will be the most stable lewis structure.

  • Formal charge = Total number of valance electrons – number of electrons remain as nonbonded – (number of electrons involved in bond formation/2)
  • Formal charge of arsenic (As): 5 – 2 – (6/2) = 0
  • Formal charge of fluorine (F) = 7 – 6 – (2/2) = 0

From the formal charge calculation, it is clear that AsF3 is a totally neutral molecule with zero charge.

AsF3 Lewis Structure Angle

Angle denotes basically the angle between two bonds. Bond angle generally depends on the two factors. They are-

  1. Hybridization
  2. Repulsion

In this molecule, the hybridization of central atom is sp3. Thus, the ideal bond angle should be 109.50. But, due to presence of lone pair- bond pair repulsion, AsF3 is deviated from its actual bond angle and show the angle (96.20) less than the actual. Due to predominance of lone pair- bond pair repulsion over the bond pair- bond pair repulsion, the actual bond angle becomes less than the ideal bond angle.

AsF3 Lewis Structure Octet Rule

Octet rule is defined as in chemistry as a very much important rule in which any molecule should have the electron configuration in its outer most shell that it resembles with the nearest noble gas valance shell electron configuration in periodic table.

In this molecule arsenic trifluoride, arsenic has five valance shell electrons. After bond formation with three fluorine atoms, arsenic gains three more electrons in its valance shell and this electron configuration matches with its nearest noble gas Krypton, Kr (4s2 4p6). Thus, octet rule is obeyed for arsenic.

Fluorine also satisfies the octet rule. It has total seven valance electron and after bond formation with arsenic it achieves eight outer most shell electrons which matches with the nearest noble gas Neon (2s2 2p6).

AsF3 Lewis Structure Lone Pairs

Lone pairs are those outer most shell electrons who have no contribution in bond formation with another molecules. They are shown around the atoms in the molecular lewis structure. These lone pairs have a significant role in structure determination of any molecule.

  • Nonbonded electron = Total number of valance electron – number of bonded electrons.
  • Nonbonded electrons of As: 5 – 3 = 2 or one lone pair.
  • Nonbonded electrons of each of the fluorine atom: 7 – 1 = 6 or three lone pairs.

Thus, the total number of nonbonded electrons in AsF3 is = [2+(6×3)] = 20

AsF3 Valence Electrons

Valance shell electrons are the outer most shell electrons of any atom. They are the most reactive due to having least nuclear attraction on them with comparing to the other inner shell electrons.

Arsenic is a nitrogen group element. Thus, it has five electrons in its valance shell. Two of them in 4s orbital and rest of the three electrons in 4p orbital having half filled electron configuration.

Fluorine is a halogen compound and all the halogen compound have seven electrons in their respective valance shell. Two of them are in 2s orbital and rest of the five are in 2p orbital.

AsF3 Hybridization

Hybridization is one of the most important factor in chemistry for determining the molecular shape. It decides the shape and the bond angle of a molecule  which is shown in the following table.

Hybridization of central atom Structure
spLinear
sp2Trigonal planar
sp3Tetrahedral
sp3dTrigonal bipyramidal
sp3d2Octahedral

In this molecule arsenic is sp3 hybridized. The hybridization of AsF3 is shown below.

AsF3 Hybridization

Arsenic has three electrons in its 4p orbital. Fluorine atom shares its one valance electron with arsenic and this sp3 hybridization is generated. Hybridization is nothing but the mixing of two atomic orbitals to generate a new hybrid orbital. In this sp3 hybridization, one s and three p orbital of arsenic participates and the percentage of s orbital is 25 and p orbital is 75. From the hybridization, we can predict that this molecule has three bond pairs with one lone pair making the molecule trigonal pyramidal.

AsF3 Solubility

Arsenic trifluoride is soluble in different type of inorganic and organic solvents like ether, benzene and ammonia solution. It is decomposed in water. It is very much reactive with water.

Is AsF3 acidic or basic?

 AsF3 is a mild basic element because of the lone pair of arsenic. Arsenic can easily donate its lone pair to any electron deficient atom, which is one of the most important properties of a lewis base. It can’t be an acid because it is not an electron deficient molecule, rather it is an electron rich molecule which acts as a electron pair donor not an acceptor.

Is AsF3 ionic?

AsF3 definitely is not an ionic compound. It is a covalent compound. In this molecule, total three covalent bonds are present between arsenic and three fluorine atoms.

In this molecule, arsenic has three p electrons and each of the fluorine atom shares their one valance electron among seven with arsenic. These electrons are shared nor completely transferred from fluorine to arsenic and the electronegativity difference between As and F is also not so high.

To be an ionic compound, one atom should be metal but in AsF3, arsenic is metalloid and fluorine is a nonmetal. Thus, it is a covalent compound not an ionic compound.

Is AsF3 polar or nonpolar?

Polarity of any molecule depends on two factors. They are-

  1. Polarity of the each bond
  2. Orientation of the bond and the atoms.

In AsF3, As-F bond is relatively polar due to small electronegativity difference between them and the structure of this molecule is trigonal pyramidal. Thus, one bond moment can’t be cancelled out by another bond.

So, all these reasons state that AsF3 is definitely a polar molecule with a permanent dipole moment.

Conclusion

The detailed explanation on the structure, bond angle, shape and other relevant topics of AsF3 are highlighted through the above article. We can see that this molecule shows a trigonal pyramidal structure with bond angle 96.20 and having two and six nonbonding electrons on arsenic and fluorine respectively.

Aditi Roy

Hi..I am Aditi Roy, I have completed my graduation from University of Calcutta and am pursuing M.Sc in Chemistry from Techno India University. My area of specialization is on Inorganic Chemistry.

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