Sulfur hexafluoride (SF6) Lewis dot structure, molecular geometry or shape, electron geometry, bond angle, formal charge
SF6 is the chemical formula of a colorless, odorless gas called sulfur hexafluoride. Its molar mass is 146.06 g/mol thus it is heavier than air. It is a very stable chemical compound at r.t.p owing to its non-combustibility and inflammability.
We have compiled for you in this article, some essential chemical properties of SF6 i.e., its Lewis structure, molecular shape or geometry, electron geometry, bond angle, hybridization, and formal charge present on it.
The Lewis structure of SF6 consists of a sulfur (S) atom and six atoms of fluorine (F). The sulfur (S) atom lies at the center of the structure. It is surrounded by 6 fluorine (F) atoms at the sides. There is a total of 6 electron pairs around the central S atom. All electron pairs are bond pairs thus there is no lone pair of electrons on the central sulfur.
Drawing the Lewis structure of SF6 is quite easy. You can also do so by following the simple steps given below.
Steps for drawing the Lewis dot structure of SF6
1. Count the total valence electrons in SF6
The Lewis structure of a chemical molecule is a simplified representation of all the valence electrons present in it. So, in order to draw the Lewis structure of SF6, we first need to find the total valence electrons present in it.
The valence electrons present in a molecule can be easily determined by identifying the concerned elements from the Periodic Table.
When you look at the Periodic Table, you will find sulfur (S) in Group VI A, so it has a total of 6 valence electrons. Fluorine (F) on the other hand, is situated in Group VII A of the Periodic Table. It is a halogen that has a total of 7 valence electrons.
∴ SF6 is made up of one sulfur and six fluorine atoms. So, the total valence electrons available to draw the Lewis structure of SF6 = 6 + 6(7) = 48valenceelectrons.
2. Find the least electronegative atom and place it at the center
Electronegativity is defined as the ability of an atom to attract a shared pair of electrons from a covalent chemical bond.
In the Lewis dot structure, we place the least electronegative atom at the center of the molecule. Owing to the central atom’s lower electronegativity, it can more readily share its electrons with the surrounding atoms.
Therefore, S is placed at the center of the SF6 Lewis structure. All the 6 F atoms are placed in its surroundings.
3. Connect outer atoms with the central atom
In this step, all the outer atoms are joined with the central atom using single bonds.
In the SF6 molecule, the 6 fluorine (F) atoms act as outer atoms while sulfur (S) is the central atom. So, all the 6 F atoms are joined to the central S using straight lines as shown in the figure below.
Each straight line represents a single covalent bond i.e., a bonded electron pair (2 electrons). There are a total of 6 single covalent bonds in the Lewis structure. Each bond represents 2 electrons, so the total valence electrons used in this structure are 6(2) = 12valenceelectrons.
Total valence electrons available – electrons used in bonding = 48-12=36valence electrons.
So, we still have 36 valence electrons available to be placed in the Lewis structure of SF6.
4. Complete the octet of outer atoms
Fluorine (F) atoms are the outer atoms in SF6. Each F atom needs a total of 8 valence electrons to achieve a stable octet electronic configuration.
Each F is bonded to the central S atom by a single bond. The S-F bond represents 2 electrons thus each F already contains 2 electrons, we need to place 6 more electrons in its surroundings to complete the octet configuration of an F atom.
These 6 valence electrons are placed as 3 lone pairs around each F atom in the Lewis structure of SF6. Refer to the dots shown in the figure below.
5. Complete the octet of the central atom
Total valence electrons used till step4= 6 bond pairs (shown as straight lines) + 6 (electrons placed around each F atom, shown as dots) = 6(2)+6(6)=48valenceelectrons.
Total valence electrons available – electrons used till step5 = 48-48= 0 valence electrons.
All the available valence electrons are already used so there is no lone pair on the central S atom.
Sulfur (S) has a total of 12 electrons surrounding it in the Lewis structure of SF6.
There is a special category of atoms that can expand their valence shell and accommodate more than 8 valence electrons. Sulfur (S) belongs to this special category. It has an expanded octet. It can accommodate more than 8 electrons during chemical bonding as it has an empty 3d subshell. So, the incoming electrons are placed in the 3d subshell after completely filling the 3p orbitals.
Finally, we just need to check the stability of the Lewis structure. We can do that by verifying whether there is some formal charge present on SF6 or not.
6. Check the stability of Lewis’s structure with the help of the formal charge concept
The less the formal charge on the atoms of a molecule, the better the stability of its Lewis structure.
The formal charge can be calculated using the formula given below.
Non-bonding electrons = No lone pair = 0 electrons
Formal charge = 6-0-12/2= 6-0-6= 6-6 =0.
In conclusion, there is no formal charge present on any of the atoms in the Lewis structure of the SF6 molecule. This ensures that it is a stable Lewis structure and we have drawn it accurately.
What are the electron and molecular geometry of SF6?
The sulfur hexafluoride (SF6) molecule has a symmetrical octahedral electron and molecular geometry. There are six bond pairs around the central S atom and no lone pair. Therefore, the molecule maintains its symmetrical octahedral shape identical to its ideal electronic geometry.
Molecular geometry of SF6
The SF6 molecule has an octahedral shape and molecular geometry. To one atom of S in the center, six F atoms are attached in a symmetrical manner. The bond pair-bond pair repulsions between six S-F bonds make the fluorine atoms occupy positions farthest away from each other. The F atoms arrange in a manner that results in an eight vertices arrangement thus the name octahedral (octa means eight) is given to the molecule.
There is no lone pair on the central S atom, so no lone pair-bond pair repulsions or lone pair-lone pair electronic repulsions exist in the molecule. Thus, the symmetrical arrangement of the F atoms at the corners of a regular octahedron stays undisturbed overall.
The molecular geometry or shape of a molecule gets influenced by the different bond pairs and lone pairs present on the central atom in the molecule. Contrarily, the electron geometry depends on the total electron pairs present on the central atom. Each electron pair, whether it’s a bond pair or a lone pair is considered a separate region of electron density.
Electron geometry of SF6
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, the ideal electronic geometry of a molecule that has a total of 6 electron pairs (i.e., 6 regions of electron density) around the central atom is octahedral. So, the electronic geometry of SF6 is also octahedral.
A straightforward way of finding the electron and the molecular geometries of SF6 is the AXN method.
AXN is a simple formula to represent the number of bonded atoms and lone pairs present on the central atom. It is used to predict the shape or geometry of the molecule using the VSEPR concept.
AXN notation for SF6 molecule
A in the AXN formula represents the central atom. In the SF6 molecule, sulfur is present at the center so A=S.
X stands for the atoms bonded to the central atom. In SF6, six fluorine (F) atoms are bonded to the central S so X=6.
N denotes the lone pairs present on the central atom. As per the Lewis structure of the SF6 molecule, there is no lone pair on S so N=0.
Thus, the AXN generic formula for the SF6 molecule is AX6.
Now have a quick look at the VSEPR chart below.
According to the VSEPR chart, the AX6 generic formula denotes an identical molecular and electron geometry i.e., octahedral.
Hybridization of SF6
The central S atom in the SF6 molecule is sp3d2 hybridized.
The electronic configuration of sulfur is 1s2 2s2 2p6 3s2 3p4.
During chemical bonding, one 3s electron of sulfur gets excited to its empty 3d orbital. Similarly, a paired 3p electron in the sulfur atom gets unpaired and shifts to another 3d orbital. Consequently, the half-filled 3s, three 3p and two 3d orbitals hybridize to yield six sp3d2 hybrid orbitals. Each of the six sp3d2 hybrid orbitals contains a single unpaired electron.
The electronic configuration of fluorine is 1s2 2s2 2p5. It has a partially filled p-orbital. The sp3d2 hybrid orbitals of S form a sigma (σ) bond with the pz atomic orbitals of F, each containing a single electron.
A shortcut for finding the hybridization present in a molecule is by using its steric number against the table given below. There are 6 electron cloud regions around the central S atom in SF6, so its steric number is 6. Thus, the SF6 molecule has sp3d2 hybridization.
Steric number
Hybridization
2
sp
3
sp2
4
sp3
5
sp3d
6
sp3d2
The bond angles of SF6
Two different bond angles are present in the SF6 molecule. The F-S-F atoms lie along a straight line at the center of the molecule forming a 180° bond angle.
Conversely, a 90° bond angle is formed at the F-S-F position where the sulfur and the fluorine atoms lie at right angles to one another. All the S-F bond lengths in the SF6 molecule are equivalent i.e., 156 pm.
SF6 has polar S-F bonds present due to an electronegativity difference between bonded S (E.N=2.58) and F (E.N=3.98) atoms.
An electronegativity difference of 3.98-2.58= 1.4 units > 0.5 units exists between the bonded atoms, so each S-F bond is polar according to Pauling’s electronegativity scale. Each S-F bond in the SF6 molecule has a specific dipole moment value (symbol μ). But it is due to the symmetrical octahedral shape of the molecule that the individual dipole moments get canceled in opposite directions.
Thus, the molecule has a uniformly distributed electron cloud over it, and it is overall non-polar with a net dipole moment μ=0.
How many lone pairs and bond pairs are present in the Lewis structure of SF6?
The Lewis dot structure of SF6 is shown below.
A sulfur (S) atom lies at the center while 6 fluorine (F) atoms are present in the surroundings.
There are six bond pairs around the central S atom. There is no lone pair present on it.
Each F atom is bonded to the central S via a bond pair while it contains three lone pairs to complete its octet configuration.
How many total valence electrons are present in the SF6 Lewis structure?
The Lewis structure of the SF6 molecule displays a total of 48 valence electrons.
There are a total of 6 bond pairs and 18lonepairs in the structure.
6(2)+18(2)= 48 valence electrons.
What is the geometry of the molecule SF6?
The SF6 molecule has an octahedral electron geometry. It is a symmetrical molecule, so its molecular geometry or shape is also octahedral.
How many bonds does sulfur tend to make?
The sulfur (S) atom belongs to Group VI A of the Periodic Table. It has a total of 6 valence electrons, so it tends to make 6 single covalent bonds in chemical molecules.
The S atom has an expanded octet so it can accommodate more than 8 valence electrons during chemical bonding. Therefore, when forming 6 single bonds as in SF6, the S atom has a total of 6(2)= 12 valence electrons.
Of PF5 and SF6, which does not have symmetrical geometry, and why?
Phosphorus (P) has a total of 5 valence electrons. All the electrons are involved in covalent bonding in the PF5 There are 5 bond pairs and no lone pair on the central P atom. So, PF5 has a trigonal bipyramidal electronic and molecular geometry.
Sulfur (S) has a total of 6 valence electrons. Six covalent bonds of S with six F atoms in the SF6 molecule form an octahedral electronic and molecular geometry. There are 6 bond pairs and no lone pair on the central S atom.
The absence of lone pairs on the central atom in each of PF5 and SF6 ensures that both the molecules have a symmetrical shape and geometry.
The total valence electrons available for drawing sulfurhexafluoride (SF6)Lewisstructure are 48.
The molecular geometry or shape of SF6 is octahedral.
The electron geometry of SF6 is also octahedral.
The molecule has an identical electron and molecular geometry because there is no lone pair present on the central S atom.
The F atoms surrounding the central S atom occupy six corners of an octahedron in a perfectly symmetrical manner.
The central S atom in SF6 is sp3d2
There are two different F-S-F bond angles in the SF6 molecule i.e., 90° and 180° respectively.
All the S-F bond lengths are equivalent i.e., 156 pm.
The polarity of individual S-F bonds gets canceled in opposite directions in the symmetrical shape of the molecule thus SF6 is a non-polar molecule with net μ=0.
There are zero formal charges present on the atoms in the SF6 molecule which accounts for the exceptional stability of its Lewis structure.
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5. Complete the octet of the central atom
