Does sif4 have an expanded octet?
Solution : Silicon has four valance electons and forms four bonds with fluorine atoms. `SiF_(4)` has octet configuration. It is an electron pair acceptor, due to the availability of empty valence d-orbitals.
It uses 4 of these 6 valence electrons to form four single bonds with the 4 fluorine atoms. The remaining 2 electrons exist as a lone pair of electrons. This means that sulfur has 10 electrons in its valence shell and thus violates the octet rule since it has an expanded octet.
EXPANDED OCTET:
This is most commonly seen with sulfur and phosphorus. As in the molecule SF₂, sulfur can follow the octet rule. Each atom has eight electrons around it. It is possible to sufficiently excite the sulfur atom to force valence electrons into the d orbital, allowing compounds like SF₄ and SF₆ to form.
Expanded octet (hypervalent): A valence shell electron count that exceeds eight electrons. In methane (CH4), carbon has a full octet (eight valence electrons). In phosphate ion (PO43-), each oxygen has a full octet (eight valence electrons), whereas phosphorus has an expanded octet (ten valence electrons).
After excitation we can see that there are now 4 unpaired electrons which means sulfur can now form 4 covalent bonds plus 1 lone pair which will give a total of 10 electrons in its valence shell. Since sulfur now has more than 8 electrons, we say that it "expands octet".
Expanded octet occurs when an atom is able to have more than 8 valence electrons. For example, in SO₃, the sulfur atom forms 6 covalent bonds, hence it has 12 valence electrons.
SF4 molecular geometry is see-saw with one pair of valence electrons. The nature of the molecule is polar. These atoms form a trigonal bipyramidal shape.
Four fluorine atoms are linked to the lone pair on the S atom in SF4 (S has 6 valence electrons; 4 of them undergo bonding with 4 Fluorine atoms while the other 2 remains as a lone pair on S atom). All of them are in hybridized orbitals. There are five orbitals in this category.
Phosphorous often has 5 orbitals (10 electrons) and sulfur often has 6 orbitals (12 electrons) because they are in the third period, but nitrogen and oxygen can never have expanded octets because they are in the second period and there is not such thing as a 2d orbital.
why ? The electronic configuration of oxygen is 1s22s22p4. This clearly indicates that oxygen is small in size and does not possess vacant orbitals to accommodate extra electrons.
How do you find the octet rule?
Connect each atom to the central atom with a single bond (one electron pair). Subtract the number of bonding electrons from the total. Distribute the remaining electrons as lone pairs on the terminal atoms (except hydrogen), completing an octet around each atom.
You can often identify expanded octet by the S = N-A rule. When this "rule" suggests that you need fewer bonds than needed to put together the skeleton structure, then you need expanded octet.
Sulfur, phosphorus, silicon, and chlorine are common examples of elements that form an expanded octet. Phosphorus pentachloride (PCl 5) and sulfur hexafluoride (SF 6) are examples of molecules that deviate from the octet rule by having more than 8 electrons around the central atom.
You can expand an octet of an atom if it is in the the 3p orbital because then it can access its 3d orbital. It is done to remove formal charge. With resonance structures, you are often trying to reduce the formal charge on each individual atom, and it often leads to accessing the d orbital to expand its octet.
SF4 Hybridization
Sulfur has four bonding pairs of electrons and one lone pair, making its total number of regions for electron density 5.
In sulfate, the sulfur is attached to four different atoms. We could draw that structure in two ways. A structure that obeys the octet rule would have a single bond to each oxygen. That would satisfy the octet of sulfur.
Sulfur has four electrons around it in this structure (one from each of its four bonds) which is two electrons more than the number of valence electrons it would have normally, and as such it carries a formal charge of +2.
There are no more than 8 electrons in its valence shell. Therefore PF3 P F 3 does not contain an expanded octet.
2) The Si in SiF4 does not follow the octet rule because fluorine is in an unusual oxidation state.
Phosphorous often has 5 orbitals (10 electrons) and sulfur often has 6 orbitals (12 electrons) because they are in the third period, but nitrogen and oxygen can never have expanded octets because they are in the second period and there is not such thing as a 2d orbital.
Is sih4 an exception to the octet rule?
These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon in CCl4 (carbon tetrachloride) and silicon in SiH4 (silane). Because hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule and only needs to form one bond.
Count the total number of electrons for the valence shell of each atom. If the number turns out to be more than 8, the atom is having an expanded octet in the molecule concerned. For example: Phosphorus atom in PCl3 doesn't possess an expanded octet but in case of PCl5 it does.