The chemical (also called IUPAC) name of SiF4 is silicontetrafluoride or tetrafluoro silane, which is a colorless toxic and corrosivecompound. There are two other names: silicon fluoride and fluoro acid air bywhich 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 silicontetrafluoride (SiF4) is a polar molecule or nonpolar molecule in full detail.But before that, you must have some ideas about what polar and nonpolar moleculesare. So, without wasting your time, let’s start…
Polar Molecules
Polar molecules are those molecules that have a net dipolemoment and this is possible only if there is an electronegativity differencebetween the atoms as well as asymmetrical geometry so that the induced dipolecharges do not cancel each other.
There are some certain conditions for the molecule to be polari.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 becauseit forms by equal sharing of electrons between the atoms in a compound and thisis what covalent bond is known for.
One more case for the nonpolar molecule if the moleculeshave symmetrical structure so that the induced partial charges on the individualatoms nullify each other and the net dipole moment becomes zero.
As these are a pure covalent bond so they are insoluble inwater (called hydrophobic) and other polar solvents but are soluble in nonpolarsolvents like carbon tetrachloride (CCl4), carbon dioxide (CO2), benzene (C6H6)etc.
Now, is SiF4 polar or nonpolar? Yes, SiF4 is a nonpolar moleculedespite four individual Si-F bonds are polar in nature. This is because SiF4has 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 conditionsfor a molecule to be polar or nonpolar in the above definitions of the polar moleculeand 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 differencebetween silicon (1.90) and fluorine (3.98) is 2.08 (According to the Pauliscale statement). But we know molecular polarity is a vector quantity whichmeans net polarity is the vector sum of individual bond dipoles.
According to the VSEPR theory, AX4E0 structured compounds tetrahedralelectronic 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-Fbond dipole charges are opposing each other, as a result, the net dipole chargeof the whole molecule becomes zero.
As shown in the above diagram, there are no lone pairs ofnonbonding electrons are present on the central Si atom. So, not any kind offorce 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 theirbonding partners at the time of bond formation. All the atoms have their ownelectronegativity value which varies from atom to atom. Some have higher EN value andsome have lower EN value.
The atoms having higher electronegativity value attract theelectrons pair from the bonding partners. It means higher the electronegativitydifference between atoms, the more uneven sharing of electrons takes place. In theperiodic table, the fluorine (F) atom has the highest electronegativity value 3.98, andfrancium (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 polaraccording 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 Siatom is in a central position surrounded by four F atoms with a bond angle of109.5°which makes the SiF4 molecule symmetrical.
Symmetrical means theforce of attraction between all four individual fluorine atoms to central siliconatom are equal and in opposite direction to each other. The induced charges onevery Si-F get cancel by each other. Thus, the SiF4 molecule has zero dipolecharge.
SiF4 has the same molecular geometrical structure as carbontetrachloride (CCl4), only different is here silicon in place of carbon andfluorine in the place of chlorine.
SiF4 Dipole Moment
The dipole moment is defined as the products of induced chargeand 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 bepolar or nonpolar. All the polar molecules have a net dipole moment and allnonpolar have zero dipole moment.
As silicon tetrafluoride has a symmetrical geometry, all theindividual dipole charges are opposed to each other, as a result, zero charges onthe molecule collectively.
And we know that from the definition of dipole moment, it isa product between charge and distance but the whole molecule has zero charges. Thisis why SiF4 has a zero dipole moment and the molecule is nonpolar.
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