Is SiF4 Polar or Nonpolar?

The chemical (also called IUPAC) name of SiF4 is silicon tetrafluoride or tetrafluoro silane, which is a colorless toxic and corrosive compound. There are two other names: silicon fluoride and fluoro acid air by which is known in the market.

In the laboratory, SiF4 is prepared by heating BaSiF6 above 300 °C which gives residue BaF2 and SiF4 in volatile form.

BaSiF6 → BaF2 + SiF4 (volatile)

In this article, we are going to know whether silicon tetrafluoride (SiF4) is a polar molecule or nonpolar molecule in full detail. But before that, you must have some ideas about what polar and nonpolar molecules are. So, without wasting your time, let’s start…

Polar Molecules

Polar molecules are those molecules that have a net dipole moment and this is possible only if there is an electronegativity difference between the atoms as well as asymmetrical geometry so that the induced dipole charges do not cancel each other.

There are some certain conditions for the molecule to be polar i.e. have asymmetrical structure, presence of lone pair of electrons, or the electronegativity difference between central atom to bonded atoms.

Polar molecules have polar covalent bonds or ionic bonds. They are soluble in water (called hydrophilic) and other polar solvents like methanol (CH3OH), ammonia (NH3), Nitrogen dioxide (NO2), etc.

Nonpolar Molecules

Nonpolar molecules are considered as a pure covalent bond because it forms by equal sharing of electrons between the atoms in a compound and this is what covalent bond is known for.

One more case for the nonpolar molecule if the molecules have symmetrical structure so that the induced partial charges on the individual atoms nullify each other and the net dipole moment becomes zero.

As these are a pure covalent bond so they are insoluble in water (called hydrophobic) and other polar solvents but are soluble in nonpolar solvents like carbon tetrachloride (CCl4), carbon dioxide (CO2), benzene (C6H6) etc.

Now, is SiF4 polar or nonpolar? Yes, SiF4 is a nonpolar molecule despite four individual Si-F bonds are polar in nature. This is because SiF4 has tetrahedral molecular geometry which means the molecule is symmetrical so that the polarities of the Si-F bonds cancel each other and the net dipole becomes zero.

Why is SiF4 a nonpolar molecule? [Detailed Explanation]

As we have already familiar, there are certain conditions for a molecule to be polar or nonpolar in the above definitions of the polar molecule and nonpolar molecule. The same things apply here which makes SiF4 a molecule.

In SiF4, there are four fluorine atoms are bonded with the central silicon atom. The Si-F bonds are polar as the electronegativity difference between silicon (1.90) and fluorine (3.98) is 2.08 (According to the Pauli scale statement). But we know molecular polarity is a vector quantity which means net polarity is the vector sum of individual bond dipoles.

According to the VSEPR theory, AX4E0 structured compounds tetrahedral electronic geometry which makes SiF4 molecular geometry. Where,

A = central atom

X = number of atoms bonded with the central atom

E = lone pair of electrons on the central atom

The molecule is symmetrical so that all the individual Si-F bond dipole charges are opposing each other, as a result, the net dipole charge of the whole molecule becomes zero.

As shown in the above diagram, there are no lone pairs of nonbonding electrons are present on the central Si atom. So, not any kind of force localized on the molecule.

Also Read: Is SiCl4 (Silicon tetrachloride) Polar or Nonpolar?

SiF4 Polar or Nonpolar (Based on polarity determining factors)

These are some of the major factors which are used to determine the polarity of the compounds:

Electronegativity difference

Electronegativity is a kind of force exerted by atoms on their bonding partners at the time of bond formation. All the atoms have their own electronegativity value which varies from atom to atom. Some have higher EN value and some have lower EN value.

The atoms having higher electronegativity value attract the electrons pair from the bonding partners. It means higher the electronegativity difference between atoms, the more uneven sharing of electrons takes place. In the periodic table, the fluorine (F) atom has the highest electronegativity value 3.98, and francium (Fr) has the lowest 0.7.

In the SiF4 compound, the electronegativity difference between fluorine (3.98) and Si (1.90) is 3.98-1.90= 2.08 which shows the Si-F bond is polar according to the Pauli scale.

SiF4 Molecular Geometry

SiF4 molecule has a tetrahedral molecular geometry. In SiF4, four Si-F bonds are formed during the molecular formation in such a way that Si atom is in a central position surrounded by four F atoms with a bond angle of 109.5° which makes the SiF4 molecule symmetrical.

Symmetrical means the force of attraction between all four individual fluorine atoms to central silicon atom are equal and in opposite direction to each other. The induced charges on every Si-F get cancel by each other. Thus, the SiF4 molecule has zero dipole charge.

SiF4 has the same molecular geometrical structure as carbon tetrachloride (CCl4), only different is here silicon in place of carbon and fluorine in the place of chlorine.

SiF4 Dipole Moment

The dipole moment is defined as the products of induced charge and distance of separation between the atoms. It is given as,

Dipole moment = Charge (Q) * distance of separation (d)

Its unit is Debye and denoted by ‘D’. 1D = 3.33564*10-30 C.m, where C is Coulomb and m is meter.

The dipole moment is the major aspect for any compound to be polar or nonpolar. All the polar molecules have a net dipole moment and all nonpolar have zero dipole moment.

As silicon tetrafluoride has a symmetrical geometry, all the individual dipole charges are opposed to each other, as a result, zero charges on the molecule collectively.

And we know that from the definition of dipole moment, it is a product between charge and distance but the whole molecule has zero charges. This is why SiF4 has a zero dipole moment and the molecule is nonpolar.

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