SiF4 is the chemical formula for silicon tetrafluoride. It is a colorless, corrosive, non-flammable, and highly toxic gas with a narrow liquid range. SiF4 has a molar mass of 104.08 g/mol.
If you are interested to know whether the silicon tetrafluoride SiF4 molecule is polar or non-polar, continue reading the article.
Is SiF4 polar or non-polar?
Silicon tetrafluoride SiF4 is a non-polar molecule. It consists of one silicon (Si) atom and four fluorine (F) atoms. The silicon is kept at the central position, and all four fluorine atoms are at the surrounding positions, making a tetrahedral molecular geometry.
An electronegativity difference of 2.08 units exists between the bonded atoms of silicon and fluorine in each Si-F bond in SiF4.
Thus, each Si-F bond is individually polar in SiF4 and possesses a specific dipole moment value (symbol µ).
However, in the SiF4 molecule, no lone pair of electrons is present on the central silicon atom; thus, no distortion is witnessed in its shape and/or geometry.
It is due to the symmetrical tetrahedral shape of SiF4 that the dipole moments of individually polar Si-F bonds get canceled equally on each side of the molecule.
Hence, the electron cloud stays uniformly distributed over the molecule. As a result, the SiF4 molecule is overall non-polar (net µ = 0).
A molecule is polar if there is a non-uniform charge distribution present in it. If the charge distribution gets equally balanced in different parts, then that molecule or molecular ion is considered non-polar.
The following three factors mainly influence the polarity of a molecule:
The electronegativity difference between two or more covalently bonded atoms
Dipole moment
Molecular geometry or shape
Now, let us discuss the effect of the above three factors one by one to prove that the silicon tetrafluoride SiF4 molecule is overall non-polar.
Factors affecting the polarity of SiF4
Electronegativity
It is defined as the ability of an elemental atom to attract a shared pair of electrons from a covalent chemical bond.
Electronegativity increases across a period in the Periodic Table while it decreases down the group.
Greater the electronegativity difference between bonded atoms in a molecule, the higher the bond polarity.
Silicon (Si) is present in Group IV A (or 14) of the Periodic Table. The electronic configuration of silicon is 1s2 2s2 2p6 3s2 3p2. As per the electronic configuration, a Si-atom has a total of 4 valence electrons, it is thus short of 4 more electrons that are required so that the silicon atom can achieve a complete octet electronic configuration.
Conversely, fluorine (F) is a halogen present in Group VII A (or 17) of the Periodic Table. The electronic configuration of a fluorine atom is 1s2 2s2 2p5. According to this electronic configuration, an F-atom has a total of 7 electrons in its valence shell; thus, it lacks only a single electron that is required in order to complete its octet shell.
In the Lewis dot structure of SiF4, there are 4 Si-F single covalent bonds. All 4 valence electrons of silicon used in covalent bonding leave behind no unbonded valence electron; thus, there is no lone pair of electrons on the central Si-atom in SiF4.
Contrarily, all four F-atoms contain three lone pairs of electrons. In this way, all the bonded atoms attain a completely stable electronic configuration via chemical bonding in SiF4.
Due to the absence of any lone pair of electrons on the central Si-atom in SiF4, there is no distortion in the symmetrical tetrahedral shape or geometry of the molecule.
Atom
Electronic configuration
Valence electrons
Silicon (14Si)
1s22s22p63s23p2
4
Fluorine (9F)
1s22s22p5
7
The electronegativity difference between a Si-atom (E. N = 1.90) and an F-atom (E. N = 3.98) in each of the four Si-F bonds in SiF4, is 2.08 units.
Hence, the fluorine atom with a higher electronegativity gains a partial negative (Fδ-) charge while the central silicon atom obtains a partial positive (Siδ+) charge.
As a result, in SiF4, all Si-F bonds are individually polar. Fluorine more strongly attracts the shared electron cloud from each Si-F bond in the silicon tetrafluoride molecule.
Dipole Moment
Dipole moment (μ) is a vector quantity that points from the positive pole to the negative pole of a bond or a molecule.
It is mathematically calculated as a product of the magnitude of charge (Q) and charges separation (r). The dipole moment is expressed in a unit called Debye (D).
The dipole moment of a polar covalent bond conventionally points from the positive center to the center of the negative charge.
So in polar bonds of SiF4, the dipole moment of each Si-F bond points from Siδ+ to Fδ-(as shown below).
Molecular geometry
According to the valence shell electron pair repulsion (VSEPR) theory of chemical bonding, SiF4 is an AX4E0 or simply AX4-type molecule. To one Si-atom at the center (A), four bonded atoms are attached (four F-atoms), and the central Si-atom contains no lone pair (E).
The molecular geometry or shape of SiF4 is thus tetrahedral, which is identical to its ideal electron pair geometry. In this symmetrical tetrahedral shape, the bonded atoms form a mutual bond angle of 109.5°.
Due to the absence of any lone pair of electrons on the central Si-atom, the symmetry of the SiF4 molecule stays undisturbed. The dipole moments of individually polar Si-F bonds get canceled uniformly in this symmetrical shape.
The charged electron cloud thus stays evenly spread over the molecule. Consequently, silicon tetrafluoride SiF4 is overall a non-polar molecule (net µ = 0).
Difference between polar and nonpolar?
Polar molecule
Non-polar molecule
Atoms must have a difference in
electronegativity
Atoms may have the same or different electronegativity values
Unequal charge distribution overall
Equal charge distribution overall
Net dipole moment greater than zero
Net dipole moment equals to zero
Examples include water (H2O), ethanol (CH3CH2OH), ammonia (NH3), sulfur dioxide (SO2), bromine trifluoride (BrF3), phosphorus trifluoride (PF3), nitrogen trifluoride (NF3), etc.
Examples include oxygen (O2), nitrogen (N2), methane (CH4), carbon disulfide (CS2), ethane (C2H6), propane (C3H8), silicon tetrafluoride (SiF4), etc.
The electronegativity difference between the bonded Si-atom (E. N= 1.90) and F-atom (E. N= 3.98) is 2.08 units. Therefore, the F-atom gains a partial negative (Fδ-) charge while the central Si-atom obtains a partial positive (Siδ+) charge in SiF4.
Each Si-F bond thus possesses a particular dipole moment.
However, it is due to the symmetrical tetrahedral shape of SiF4 that the individual Si-F dipole moments get canceled. The electron cloud stays uniformly distributed in the molecule overall.
Thus, SiF4 is overall a non-polar molecule with net µ = 0.
Does the non-polar SiF4 molecule contain polar bonds?
Yes, each Si-F bond in the silicon tetrafluoride SiF4 molecule is polar due to a high electronegativity difference of 2.08 units between the bonded Si-atom (E. N = 1.90) and F-atom (E.N = 3.98).
Still, having a symmetrical tetrahedral molecular shape and geometry, SiF4 is overall non-polar.
Why is SF4 polar while SiF4 is non-polar?
SiF4 is non-polar while SF4 is a polar molecule.
In SiF4, the central Si-atom uses all of its valence electrons for covalent bonding. There is no lone pair on Si-atom and SiF4 has a symmetrical tetrahedral molecular shape.
Consequently, the dipole moments of individually polar Si-F bonds get canceled in opposite directions; thus, it is overall non-polar (net µ =0).
On the other hand, in SF4 four F-atoms are bonded to an S-atom. The central sulfur atom uses only 4 of its valence electrons for bonding out of the 6 initially available.
This results in a lone pair of electrons on the central S-atom in SF4. The lone pair-bond pair repulsions lead to an asymmetric seesaw shape of the SF4.
The dipole moments of individually polar S-F bonds do not get canceled in this asymmetrical shape. Consequently, SF4 is overall a polar molecule (net µ =0.632 D).
Is there a formal charge on the bonded atoms in the SiF4 molecule?
Formal charge of an atom = [ valence electrons – non-bonding electrons- ½ (bonding electrons)]
All atoms in theSiF4 molecule including silicon and fluorine obtain a formal charge equal to zero.
Hence, the overall charge present on the silicon tetrafluoride molecule is also zero.
Summary
Silicon tetrafluoride (SiF4) is a non-polar molecule.
It consists of four Si-F bonds.
Si-F bonds are highly polar, with an electronegativity difference of 2.08 units between the bonded Si-atom (E. N= 1.90) and F-atom (E. N= 3.98).
Silicon tetrafluoride SiF4 has a tetrahedral molecular and electron geometry with a mutual bond angle of 109.5° between the bonded atoms.
Due to the absence of any lone pair of electrons on the central Si-atom, the SiF4 molecule has a symmetrical tetrahedral molecular geometry and shape.
The dipole moments of individually polar Si-F bonds get canceled uniformly in the symmetrical shape. The charged electron cloud stays evenly spread over the molecule.
The net dipole μ in SiF4 is thus zero, and silicon tetrafluoride is overall a non-polar molecule.
Vishal Goyal is the founder of Topblogtenz, a comprehensive resource for students seeking guidance and support in their chemistry studies. He holds a degree in B.Tech (Chemical Engineering) and has four years of experience as a chemistry tutor. The team at Topblogtenz includes experts like experienced researchers, professors, and educators, with the goal of making complex subjects like chemistry accessible and understandable for all. A passion for sharing knowledge and a love for chemistry and science drives the team behind the website. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/
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