Chapter 3: – Chemical Bonding
B.sc 1st year Book (Page 13)
Hybridization of atomic orbitals
Hybridization means the mixing of atomic orbitals. It is a very important theoretical concept given to explain the formation and geometry of molecules. It is assumed that before bond creation, the atomic orbitals of an atom mix up together (according to the requirement) and redistribute their energies. On account of this redistribution of energy, a set of the same member of new orbitals is obtained. The orbitals thus obtained are of equal energy and are critical in all respect. These new orbitals are called ‘mixed orbitals’ or ‘hybrid orbitals’ and the phenomenon is called Hybridization.
Since hybrid orbitals are of equal energy and identical in all respect, therefore the covalent bonds formed by them will also be identical in all respect. Thus, in order to facilitate the formation of equivalent covalent bonds in BeCl2, BF3, CH4, PCl5, SF5, and other covalent molecule it is necessary that the atomic orbitals of the central atom taking part in bond formation must be identical in all respects.
Case of Hybridization :
They know that p-orbitals are directed in space 1.73 times more than s-orbital. It is, therefore, the bond formed by p-orbital should be 1.73 times stronger than that formed by s-orbital. Also, the three p-orbitals are equivalent in all respect except in orientation. Hence, the bond formed by them should be equally stronger having a bond angle equal to I Since a 2 s-electron is present in each of the 3 elements: Be, B, and C, one bond. ned by 2 s-electron from pure 2s-orbital must be different from the remaining bonds ned by pure p-orbitals. But it is not actually so. However, it is found experimentally that in -pounds of beryllium, boron, and carbon all bonds are equivalent, and the bond angles = are never equal to 90′. This clearly explains that just before bond formation all the bonding orbitals in these elements must be equivalent in all aspects except in orientation. Thus, e problem of this type has been solved by the introduction of the concept of hybridization by Pauling in 1931.
According to Pauling, hybridization is a Mathematical concept in which a new set of -rich orbitals so-called hybrid orbitals is constructed from intermixing of pure atomic orbital by an atom. In other words, the hybridized state is the valence state of an atom. The valence state of an atom is completely imaginary and denotes the state when the an is ready to form bond8. Thus, hybridization is defined as the process of premixing atomic orbitals of comparable energies and the formation of a set of the same -number of new orbitals of equivalent energies” size, and shape.
Why do the hybrid orbitals form Stronger bonds?
Atomic orbitals prefer to hybridize because the bond formed by the hybrid orbitals are more stable as compared to the bonds formed by pure atomic orbitals. This is because E hybrid orbitals are more directional as compared to the pure atomic orbitals and hence EF is capable of participating to a greater extent in overlapping to form stronger bonds. For – parison, relative bond strengths of various orbitals are shown in table 3.6 given below.
Conditions for Hybridization:
Following rules have been Framed for an atom to undergo hybridization.
(i) The atomic orbitals taking pan in hybridization should be of comparable energy i.e there should be only a small difference in their energies.
(ii) The electrons present in the atomic orbitals are never involved in hybridization. In other words, it is the orbitals that undergo hybridization and not the electrons. Hence: completely filled, half-filled, and even empty orbitals may take part in hybridization. Bua the arrangement of electrons in hybrid orbitals remains the same as that appears in atomic orbitals before hybridization.
(iii) The number of hybrid orbitals produced is always the same as the number of atoms orbitals taking part in hybridization.
(iv) Once an orbital has been used to build a hybrid orbital it is then no longer available t. hold electrons in their pure form.
(v) Hybrid orbitals form a stronger bonus than the pure atomic orbitals from which they are formed.
(vi) The hybrid orbitals repel each other and try to keep themselves as far as possible. means, the type of hybridization, can tell about the bond angles and structures of molecules.
(vii) Various types of hybridization are differentiated either by indicating the genomes constituted by the hybrid orbitals or by indicating the number and type of atom. orbitals taking part in hybridization. For example, the hybridization involving one s- act three p-orbitals is known as tetrahedral or spa hybridization.
(ii) The electrons present in the atomic orbitals are never involved in hybridization. In other words, it is the orbitals that undergo hybridization and not the electrons. Hence: completely filled, half-filled, and even empty orbitals may take part in hybridization. Bua the arrangement of electrons in hybrid orbitals remains the same as that appears in atomic orbitals before hybridization.
(iii) The number of hybrid orbitals produced is always the same as the number of atoms orbitals taking part in hybridization.
(iv) Once an orbital has been used to build a hybrid orbital it is then no longer available t. hold electrons in their pure form.
(v) Hybrid orbitals form a stronger bonus than the pure atomic orbitals from which they are formed.
(vi) The hybrid orbitals repel each other and try to keep themselves as far as possible. means, the type of hybridization, can tell about the bond angles and structures of molecules.
(vii) Various types of hybridization are differentiated either by indicating the genomes constituted by the hybrid orbitals or by indicating the number and type of atom. orbitals taking part in hybridization. For example, the hybridization involving one s- act three p-orbitals is known as tetrahedral or spa hybridization.
Related Topic | Chemical Bonding |
Types of hybridization :
1- sp hybridization or linear hybridization:
This type of hybridization involves the mixing of one s and one p-orbital of valence shell the central atom to form two sp hybrid orbitals as follows ;
Characteristics of sp-hybrid orbitals :
1- sp hybrid orbitals are symmetrical in shape and have equal energies
2- These hybrid orbitals are co-linear i.e. angle between the hybrid orbitals is 1802.
3- The normalized wave function of these hybrid orbitals may be written as :
2- These hybrid orbitals are co-linear i.e. angle between the hybrid orbitals is 1802.
3- The normalized wave function of these hybrid orbitals may be written as :
![ψspa=12[ψs+ψpp] and ψspb=12[ψs−ψpx]](https://www.bscbooks.com/wp-content/uploads/2022/06/p134b.jpg){kind=small}
4- Each sp-hybrid orbital is stronger than both pure s and p-orbitals from which it begins 5- Its predicted relative overlapping power is 1.93.
For example: In the BeCl2 molecule beryllium is the central atom which utilizes its two half-filled sp hybrid orbitals that overlap with hall-filled 3pz atomic orbitals of two chlorine atoms to form two Be−Cl, s-bonds. Both these bonds are co-planar and are at an angle 180∘ to each other Thus, BeCl, the molecule is linear as shown below.
Other molecules in which sp hybridization occurs are CO2.H−C≡N, CO, HC≡CH, etc.
2- sp2 hybridization or Trigonal planar hybridization :
In this type of hybridization one s and two p-orbitals of the valence-shell of the central atom of the given molecule are mixed together to form three sp 2-hybrid orbitals as shown below:
Characteristics of sp2 hybrid orbitals :
1- All the three sp2- hybrid orbitals are equivalent in shape and energy.
2- The lobes of sp2− hybrid orbitals are directed towards the comers of a regular triangle. The bond angles between these lobes are 120∘.
3- Since in this case contribution of p-orbitals is more hence it is less oval than sp-hybrid orbitals. As usual in this case, also one hybrid orbital is bigger while another one is smaller and it forms a stronger bond.
4- Its relative power of overlapping is 1.99 with respect to s-orbital.
5- The normalized wave function of these hybrid orbitals may be given as :
BF3 molecule:
In this molecule boron is the central atom that undergoes sp² hybridization in its excited state. Its three half-filled sp hybrid orbitals overlap with half-filled 2pz atomic orbitals of three fluorine atoms to form three B−Fσ – bonds. Thus, the shape of the BF3 molecule is triangular planar.
Structure :
3- sp3 hybridization or Tetrahedral hybridization:
The mixing of one s and three p-orbitals of the valence shell of an atom and the formation of four hybrid orbitals of equal energies is called ‘sp’ hybridization’. The lobes of sp3 hybrid orbitals are directed towards the corners of a regular tetrahedron hence, the angle between the lobes is 109∘28′as shown below:
Characteristics of sp3 hybrid orbitals :
1- All the four sp3 hybrid orbitals are symmetrical and of equal energy.
2- The relative power of overlapping is 2.00. This shows that sp3 hybrid orbitals are stronger than sp andsp2 hybrid orbitals.
3- Since sρ3 hybrid orbitals consist of75%p-character, hence its shape is almost the same as that of the pure-p-orbitals except that the bigger lobe in the sp3-hybrid orbital is somewhat broader and this orbital is shorter in length than the p-orbital.
4- The radial (normalized) wave function for the foursp3 hybrid orbitals are :
2- The relative power of overlapping is 2.00. This shows that sp3 hybrid orbitals are stronger than sp andsp2 hybrid orbitals.
3- Since sρ3 hybrid orbitals consist of75%p-character, hence its shape is almost the same as that of the pure-p-orbitals except that the bigger lobe in the sp3-hybrid orbital is somewhat broader and this orbital is shorter in length than the p-orbital.
4- The radial (normalized) wave function for the foursp3 hybrid orbitals are :
Example: Some moleculesflons which involve sp3 hybridization are CH4,CCl4,CH2Cl2,CH3Br1,NH4+ etc. (σ+ bords =4, Ip σ=0, totrahedral shape) : NH3,PH3,NX3,PX3,H3O+ etc( σ – bonds =3, lp=1, trigonal pyramidal shape) ; H2O,H2 S,SCl2 etc. ( σ – bonds m 2, lp m2, V-shape).
CH4 molecule :
In this molecule, carbon is the central atom that undergoes sp3 hybridization in its excited state. Its four hail-tiled sp3 hybrid orbitals overlap with half-filled is atomic orbitals of 4 hydrogen atoms to form four C−Hα – bonds. Thus, the shape of the CH4 molecule will be regular tetrahedral and H.C-H bond angles equal to 109∘28′ as discussed below:
Type of molecules and ions which undergo sp3 hybridizations:
(a) AB type of molecules :
In this type of molecule, A is the central atom which is surrounded by 3 lone pairs and one bond pair. According to VSEPR theory, lone pairs occupy any three sp³ hybrid orbitals. Thus, the spatial arrangement of four sp 3 hybrid orbitals around the central atom (A) is tetrahedral. Since lone pairs do not responsible for the geometry of the molecule hence AB molecules have a linear shape.
(b) AB2 type of molecules or Ions:
In such types of molecules or ions ‘A’ is the central atom which is surrounded by two lone pairs (Ip’s) and two bond pairs (bp’s). Hence atom ‘A’ undergoes sp hybridization. According to. VSEPR theory, lone pairs occupy any two sp3 hybrid orbitals. Thus, the spatial arrangement of four SPS hybrid orbitals around the central atom is tetrahedral. The shape of AB2 molecules or ions is therefore V-shaped.
Example are : H2O,OF2,NH2−SO2,SCl2,ICl2+,BrF2+etc.
H2O molecule: In the H2O molecule, the oxygen atom is the central atom, It undergoes sp3-hybridizations as follows :
It is clear from the above electronic configuration that the oxygen atom has two full-filled sp hybrid orbitals and the remaining two half-filled sp 3 hybrid orbitals. Its two half-filled sp3 hybrid orbitals overlap with a half-filled 1 s atomic orbital of two hydrogen atoms to form an H2O molecule as shown below:
It is clear from the above electronic configuration that the oxygen atom has two full-filled sp hybrid orbitals and the remaining two half-filled sp 3 hybrid orbitals. Its two half-filled sp3 hybrid orbitals overlap with a half-filled 1 s atomic orbital of two hydrogen atoms to form an H2O molecule as shown below:
(c) AB3 type of molecules or ions:
In this type of molecule or ion also A is the central atom. It is surrounded by one lone pair and three bond pairs. Hence, atom A undergoes sp3 hybridizations. According to VSEPP theory, lone pairs occupy any one of the four sp3 hybrid orbitals. The spatial arrangement of four sp3 hybrid orbitals around the central atom (A) is tetrahedral. The geometry of AB3 molecules or ions is, therefore, trigonal pyramidal.
Example : NH3,PH3,NX3,PX3,AsX3,SbCl3,H3O+,SbF3 etc
NH3 molecule: in the NH3 molecule, the nitrogen atom is the central atom. It undergoes sp3-hybridizations as follows:
It is clear from the above electronic configuration that out of four sp3 hybrid orbitals one sp3 hybrid orbital is occupied by one lone pair of electrons (lp) and the remaining three sp3 hybrid orbitals are half-filled. These three half-filled orbitals overlap with the half-filled 1s atomic orbital of three H atoms to form the NH3 molecule. In this molecule, the HNH bond angle is 107.5∘. The decrease in bond angle from 109∘28′ is due to the presence of IP electrons as shown below:
(b) AB4 type of molecules or ions :
In the AB4 type of molecules, the central atom ‘ A ‘ is surrounded by four σ-bond pairs without any lone pair of electrons. Therefore, such type of species has tetrahedral geometry as shown in figure 3.24.
Examples are: BeH4,2−,BX4(X=H1 F);CX4(X=H,Cl),NH4,2,PO4,3−,SO4,2−,ClO4−NiCl4]2−,[AlH4]−etc.
NH4 +ion: In this ion, the nitrogen atom is the central atom. It undergoes sp 3 -hybridization. Its three half-filled sp3 hybrid orbitals overlap with hall-filled 1s atomic orbitals of three hydrogen atoms to form three N−H, bonds whereas its remaining full-filled sp 3 hybrid orbital overlaps with the empty is atomic orbital of H+ion to form N⟶H+coordinate bond i.e. nitrogen utilizes its full-filled sp 3 hybrid orbitals (lp) in a donation to proton; H+ ion:
Thus, the structure of ammonium ion, NH4+ion is tetrahedral.
Thus, the structure of ammonium ion, NH4+ion is tetrahedral.
dsp² Hybridization :
The lobes of four dsp2 hybrid orbitals formed from one d, ones, and two 2p orbitals are directed towards the apices of a square. The molecule formed from such an atom would be planar with a bond angle of 90∘.
For example, in [Ni(CN)4]2− ion, Ni2+ ion has 3d8. configuration. Here, one (n−1)d− orbital is made available for hybridization by the rearrangement of electrons.
This d-orbital with one s and two p-orbitals forms four ds2 hybrid orbitals.
This d-orbital with one s and two p-orbitals forms four ds2 hybrid orbitals.
Structure :
dsp3 or sp3d Hybridization or Trigonal-bipyramidal hybridization:
When one s-orbital, three p-orbitals (px, py, pz) and one d-orbitals (dz2) of the central atom in a molecule mix together to form a set of five orbitals of equal energy. This mixing of orbitals
Characteristics of dsp3 or sp3d hybrid orbitals :
1- The lobes of hybrid orbitals are directed towards the comer of a regular pentagonal bipyramid. The angles are 90∘,120∘ , and 180∘ respectively as shown in figure 3.25,
2- Out of the five orbitals, three hybrid orbitals lie in an equatorial position at an angle of 120∘ and form an equilateral triangle whereas the remaining two orbitals occupy the perpendicular position to the plane of the triangle and are called axial or polar hybrid orbitals. Thus, these two equivalent orbitals make an angle of 180∘ which each other.
3- The three equatorial hybrid orbitals are smaller than axial hybrid orbitals.
Examples: Some common molecules or ions that are formed by sp3’d hybridization are:
(i) PX5 (σ-bonds =5,ip=0, trigonal bipyramidal shape)
(ii) SF4(σ bonds =4,lp=1, distorted trigonal bipyramidal shape)
(iii) CIF3,BrCl3,IBr3 ( σ-bonds =3,lp=2, T-shaped) and ( W ) XeF2,1Cl2 – T-bonds =2, lp=3, linear shape) etc. In Fe(CO)5dsp3 hybridization occurs.
(i) PX5 (σ-bonds =5,ip=0, trigonal bipyramidal shape)
(ii) SF4(σ bonds =4,lp=1, distorted trigonal bipyramidal shape)
(iii) CIF3,BrCl3,IBr3 ( σ-bonds =3,lp=2, T-shaped) and ( W ) XeF2,1Cl2 – T-bonds =2, lp=3, linear shape) etc. In Fe(CO)5dsp3 hybridization occurs.
Type of molecules that undergo sp3d hybridization :
AB5 type of molecules :
In such type of molecule central atom, a is surrounded by only five bond pairs (bp’s). It undergoes sp3 d hybridization and the AB5 molecule has a trigonal bipyramidal shape.
Example:
PCl5 molecule:
In this molecule, the P-atom is the central atom that undergoes sp3 d hybridization. It is clear from the following electronic configuration,
It is clear from the above electronic configuration that in the formation of PClSmolocule P-atom comes in an excited state and forms five halt-filled 5p3 d hybrid orbitals. These five hall-filled hybrid orbitals are directed towards the comers of trigonal bi-pyramid., P-atom utilizes all of these half-filled sp3 d3 hybrid orbitals in overlapping with five half-filled 3pz atomic orbitals of five Chatoms to form five P-Cl, o-bonds in as shown below:
Fig. 3.27: (a) Orientation of five sp3d hybrid orbitals (b) Head-to-head overlapping of half-filled sp3d in hybrid orbitals of P-atom with a half-filled 3pz-atomic orbital of five Cl-atoms and the formation of five sp2 d−p o-bonds (c) PC5 molecule with Trigond bipyramidal shape.
AB4 type of molecules or ions:
Such types of molecules have four bond pairs and one pair and are represented as –
Thus, A is the central atom which is surrounded by four bps and one Ip. On the basis of VSEPR theory the molecule will be stable only when the lone pair of electrons occupy any one of three basal positions of sp 3d hybrid orbitals, this causes distortion in the molecule and it acquires a structure of distorted trigonal bipyramidal SF4, SeF4, FF4+, ClF4+, BrF4+ are few examples of such molecules.
SF4 molecule:
In this molecule, the S-atom is the central atom that undergoes sp3 d hybridization. This is possible when the sulfur atom is excited and therefore one of its 3p Electrons jumps to 3dz2-orbital. Consequently, in order to share with four F-atoms, S-atom Takes available four halt-filled sp3 d hybrid orbitals as follows :
It is clear from the above electronic configuration that S-atom has four half-tilled sp3d hybrid orbitals and one full-filled sp3d hybrid orbital (lone pair). Thus, out of five sp3 d hybrid orbitals, one full-filled $p3d hybrid orbital occupies an equatorial position since according to VSEPA theory, the lone pair-bond pair repulsion is minimum. Four half-filled sp3 d hybrid orbitals of S-atom overlap with four 2pz half-filled orbitals of four F-atoms to form an SF4 molecule. Due to the presence of a 1SFSF4 molecule has a distorted trigonal bipyramidal shape and bond angles are 89∘ and 177∘ instead of being 90∘ and 180∘ respectively.
It is clear from the above electronic configuration that S-atom has four half-tilled sp3d hybrid orbitals and one full-filled sp3d hybrid orbital (lone pair). Thus, out of five sp3 d hybrid orbitals, one full-filled $p3d hybrid orbital occupies an equatorial position since according to VSEPA theory, the lone pair-bond pair repulsion is minimum. Four half-filled sp3 d hybrid orbitals of S-atom overlap with four 2pz half-filled orbitals of four F-atoms to form an SF4 molecule. Due to the presence of a 1SFSF4 molecule has a distorted trigonal bipyramidal shape and bond angles are 89∘ and 177∘ instead of being 90∘ and 180∘ respectively.AB3 type of molecules or ions:
In this type of molecule or ion, ‘A’ is the central atom which is surrounded by three bp’s and two Ip’s. On the basis of VSEPR theory both the lone pairs occupy two basal positions of spa3d hybrid orbitals which results in minimum repulsion between the ep’s at is because the angles between two Ip’s and bp’s are as far as possible i.e. 120∘. Due to which molecule becomes most stable. The molecules or ions of the type AB3(|p)2 or [AB3]+(lp)2 have a T-shaped structure.
Examples: CIF3, BrF3, IF3, etc all have T-shaped structures.
ClF3 molecule: In this molecule chlorine is the central atom which undergoes sp3 d hybridization as shown below:
From the above hybridization scheme it is evident that central atom Cl consists of two filled sp3d hybrid orbitals ( (p′s) and three half-filled sp 3 d hybrid orbitals. For minimum repulsion between the electron pairs two Ip’s occupy the basal positions and out of three remaining half-filled sp 3 d hybrid orbitals, one occupies the basal position and two along with axial positions. These half-filled sp3 d hybrid orbitals of Cl-atom overlap with singly filled 2pz orbital of three F-atoms to give the following structure:
From the above hybridization scheme it is evident that central atom Cl consists of two filled sp3d hybrid orbitals ( (p′s) and three half-filled sp 3 d hybrid orbitals. For minimum repulsion between the electron pairs two Ip’s occupy the basal positions and out of three remaining half-filled sp 3 d hybrid orbitals, one occupies the basal position and two along with axial positions. These half-filled sp3 d hybrid orbitals of Cl-atom overlap with singly filled 2pz orbital of three F-atoms to give the following structure:
Fig. 3.29: (a) Head-to-head overlapping of half-filled spd3 hybrid orbitals of Cl-atom with a hall-filed 2pz-atomic orbital of three F-atoms and the formation of sp3d−p3 a-bonds (b) CIF, a molecule with T-shape.
AB2 type of molecules or ions :
Such types of molecules of Ions have three lp’s and two bp’s. Both the bond pairs (bp’s) occupy axial positions in five sp³d hybrid orbitals and three Ip’s occupy three basal positions as shown in the figure given below:
Since the throe Ip’s occupy three basal hybrid orbitals and do not involve in overlapping hence the shape of the molecule is linear.
Example: ICl2-, I3-, ClF2−, IBrCl−; XeF2, etc all have linear shapes.
ICl2− Ion :
This ion has a symmetrical linear shape which results from sp3d hybridization of l-atom. in ICl2− ion, the iodine atom can be regarded as having 8 valence electrons. The Lowis structure of ICl2−Ion therefore becomes :
This ion has a symmetrical linear shape which results from sp3d hybridization of l-atom. in ICl2− ion, the iodine atom can be regarded as having 8 valence electrons. The Lowis structure of ICl2−Ion therefore becomes :
Fig. 3.32: Combination of ones– three p– and two d-orbitals in d2sp3 or sp3d2 hybridization and the location of six sp3d2-hybrid orbitals.
Characteristics of sp3d2 hybrid orbitals :
(i) The lobes of sp3d2 hybrid orbitals are directed toward the corners of a regular octahedron. Thus this hybridization gives regular octahedral geometry.
(ii) In this geometry, four of the orbitals are coplanar and constitute a square and the remaining two orbitals occupy the position above and below the plane of the square.
(iii) The four coplanar hybrid orbitals are smaller and equivalent whereas the remaining two axial hybrid orbitals are equivalent and longer.
(iv) Each bond angle between two adjacent hybrid orbitals is 90∘.
(v) The normalized wave functions of these hybrid orbitals are :
(ii) In this geometry, four of the orbitals are coplanar and constitute a square and the remaining two orbitals occupy the position above and below the plane of the square.
(iii) The four coplanar hybrid orbitals are smaller and equivalent whereas the remaining two axial hybrid orbitals are equivalent and longer.
(iv) Each bond angle between two adjacent hybrid orbitals is 90∘.
(v) The normalized wave functions of these hybrid orbitals are :
Note: d2sp3 type of hybridization is very common among the low spin octahedral complexes of translation metal ions.
![Example: ∣Cr(NH3)6]3+,[Mn(CN)6]3−,∣Fe(CN)6]3−,⌊Fe(CN)6]2−,[Co(NH3)6]3+](https://www.bscbooks.com/wp-content/uploads/2022/06/p150b.jpg)
The molecules or ions having sp3d2 hybridization are of the type :AB6, AB5, AB4 with six bp’s+1p=0; five bp′s+1p=1; and fourbp′s+1p′s=2 respectively as discussed as follows:AB6 type of molecules or ions or Regular octahedral species :
![Example: ∣Cr(NH3)6]3+,[Mn(CN)6]3−,∣Fe(CN)6]3−,⌊Fe(CN)6]2−,[Co(NH3)6]3+](https://www.bscbooks.com/wp-content/uploads/2022/06/p150c.jpg){kind=small}
are the examples in which the central atoms undergo sp3d2 hybridization. Such molecule’s Orions consist of bp′s=6 and Ip=0, thus, according to VSEPR theory, they have regular octahedral geometry.SF6 molecule: In this molecule, the S-atom is the central atom that undergoes sp3d2 hybridization, It is clear from the following electronic configuration :
It is clear from the above configuration that in the formation of SF6 sulfur-atom comes in a second excited state and forms six halt-tilled sp3d2 hybrid orbitals when it’s one3s, three 3p, and two 3 d orbitals are mixed together. These six hall-filled sp3 d2 hybrid orbitals are directed towards the corners of a regular octahedron. S-atom utilizes all these half-filled sp3d2 hybrid orbitals in overlapping with six hall-filled 2pz atomic orbitals of six F-atoms to form an SF6 molecule.
Figure. 3.33 : (a) Head to head overlapping to half-filled sp3d2 hybrid orbitals of S-atom with a half-filled 2pz-atomic orbital of six F-atoms and the formation of six sp3d2⋅p, S−F, σ- bonds (b)SF6 molecule with regular octahedral shape.
AB5 type of molecules or ions/or Square pyramidal species :
In this type of molecule or ions, the central atom is surrounded by five s bp’s and one lone pair. The tour s bp’s orbitals occupy along with comers of the square plane and one axial position of a regular octahedron. The next axial position is occupied by lone pair of electrons as shown in fig. 3.33. Thus, the structure of such molecules or ions is square pyramidal.
Example: The example of such species are FF5, BrF5, CIF5, [SbF5]2−, etc.
In the AB5 molecule, atom A is the central atom. Lewis structure of this molecule is –
In the AB5 molecule, atom A is the central atom. Lewis structure of this molecule is –
Overlapping of orbitals in AB5 molecule: Examples are: IF5, ICl5, BrF5, etc.
Fig. 3.34: (a) Head-to-head overlapping of half-filled sp3d2 hybrid orbital of A-atoms with half-filled npz– atomic orbital of B-atom and the formation ofsp3d2⋅p, sigma-bond (b) AB5 a molecule with a square pyramidal shape.
BrF5 molecule: In this molecule, Br-atom is the central atom that undergoes sp3d2 hybridization. It is clear from the following electronic configuration :
It is clear from the above electronic configuration that Br-atom has five half-filled sp3 d2 hybrid orbitals, and one lull-filledsp3d2 hybrid orbital occupies the axial position Since in this case the Ip’ – bp repulsion is minimum. Five half-filled sp3d2 hybrid orbitals of bromine atom overlap with five hall-filled 2pz atomic orbitals of five fluorine atoms to form a BrF5 molecule. Due to the presence of an Ip BrF5. the molecule has a square pyramidal shape.
Fig. 3.35 (a) Head-to-head overlapping of half-filled sp3d2 hybrid orbitals of Br-atom with a halt-filled 2pz-atomic orbital of free F-atoms and the formation of f(vesp3 d2−P, Br−F, s-bonds.
(b) BrF5 molecule with a square pyramidal shape.
AB4 type of molecules or ions /or Square planar species :
in such molecules or ions, the central atom is surrounded by four bp’s and two lp’s. The s bond pair orbitals occupy the position along with the four corners of a square plane and two orbitals containing Ip’s occupy the axial positions above and below the plane of square. Thus, the molecules or ions containing bp’s =4 and p’s =2 have a square planar structure as shown in figure 3.36. For example, The molecule or ions of such type are XeF4, BrF4−IF4−1Cl4− etc.
in such molecules or ions, the central atom is surrounded by four bp’s and two lp’s. The s bond pair orbitals occupy the position along with the four corners of a square plane and two orbitals containing Ip’s occupy the axial positions above and below the plane of square. Thus, the molecules or ions containing bp’s =4 and p’s =2 have a square planar structure as shown in figure 3.36. For example, The molecule or ions of such type are XeF4, BrF4−IF4−1Cl4− etc.
XeF4 molecule: The Lewis structure of this molecule is
Hence,
It is obvious from the above hybridization scheme that in six equivalent sp3 g2 hybrid orbitals two-hybrid orbitals have a lone pair of electrons each, while the remaining four are half-filled which involve overlapping with 4 hall filled p-orbitals of 4 fluorine atoms to form four sp3 d2−p1 Xe-F –bonds, It is therefore due to presence of lp’s on axial positions XeF4 molecule is not regular: octahedral but it is square planar as shown in figure 3.36given below :
Fig. 3.36 : (a) Overlapping of lour half-filled sp3d2 hybrid orbitals of X θ-atom with hall-filled 2pz-orbitals of four F-atoms. (b) Structure of XeF4
d3sp3 or sp3d3 hybridization:
In this type of hybridization one s-, three p -, and three-d-orbitals (I.e.dxy, dyz, and dxz ) are mixed to form seven hybrid orbitals of equivalent energies as shown below
Fig. 3.37: Combination of one s-, three p–, and three-d-orbitals in sp2d3hybridization and the formation of seven sp3d3. hybrid orbitals.
Characteristics of sp3 d3 hybrid orbitals :
(i) The seven sp3 d3 hybrid orbitals are directed towards the corners of a pentagonal bipyramid.
(ii) All these hybrid orbitals do not lie in one plane i.e, they are not of the same type but they can be divided into two sets of non-equivalent orbitals.
(iii) Five of these orbitals are coplanar and form a regular pentagon and the remaining two orbitals lie above and below the plane of the pentagon.
(iv) The angle between any two adjacent coplanar hybrid orbitals is 72∘and between two axial hybrid orbitals is 180∘ whereas the angle between basal and axial hybrid orbitals is 90∘.
(i) The seven sp3 d3 hybrid orbitals are directed towards the corners of a pentagonal bipyramid.
(ii) All these hybrid orbitals do not lie in one plane i.e, they are not of the same type but they can be divided into two sets of non-equivalent orbitals.
(iii) Five of these orbitals are coplanar and form a regular pentagon and the remaining two orbitals lie above and below the plane of the pentagon.
(iv) The angle between any two adjacent coplanar hybrid orbitals is 72∘and between two axial hybrid orbitals is 180∘ whereas the angle between basal and axial hybrid orbitals is 90∘.
Thus, an sp3d3 hybridized atom Is capable of forming seven s bonds. Consequently, the shape of such a molecule would be pentagonal bipyramidal (see figure, 3.38).
The sp3d3 hybridization occurs in the following types of molecules : Example: AX7 type of Interhalogen molecules such as IF7 and AX6 type of compound such as. XEF6.
(I) AB7 type of species: In such type of molecule, A is the central atom. It is surrounded by seven bond pairs (bp’s) only hence it undergoes sp3d3 hybridization. Thus, the shape of the AB7 molecule is regular pentagonal bipyramidal. IF7 is a good example of this type of molecule in which the iodine atom is assumed to be sp3 d3 hybridized and the shape of the IF7 molecule is pentagonal bipyramidal. It is evident from the following explanation:
The Lewis structure of the IF7 molecule is :
(I) AB7 type of species: In such type of molecule, A is the central atom. It is surrounded by seven bond pairs (bp’s) only hence it undergoes sp3d3 hybridization. Thus, the shape of the AB7 molecule is regular pentagonal bipyramidal. IF7 is a good example of this type of molecule in which the iodine atom is assumed to be sp3 d3 hybridized and the shape of the IF7 molecule is pentagonal bipyramidal. It is evident from the following explanation:
The Lewis structure of the IF7 molecule is :
Fig. 3.38 : (a) Head-to-head overlapping of half-filled sp3 d3 hybrid orbital of I-atom with a hall-filled 2pz-atomic orbital of seven F-atoms and the formation of sp3 d3.p,σ-bonds.
(b)F7 molecule with Pentagonal bipyramidal shape.
AB6 type of species :
These types of compounds have Distorted octahedral geometry. Such type of molecules are XeF6,IF6−TeCl62−,SbF63− etc. Which have 6bps and one Ip. Hence, the central atom undergoes sp3d3 hybridization. Theoretically, it was observed that a lone pair occupy an axial position of pentagonal bipyramid hence the molecule becomes distorted pentagonal bipyramidal as shown in figure 3.39.
These types of compounds have Distorted octahedral geometry. Such type of molecules are XeF6,IF6−TeCl62−,SbF63− etc. Which have 6bps and one Ip. Hence, the central atom undergoes sp3d3 hybridization. Theoretically, it was observed that a lone pair occupy an axial position of pentagonal bipyramid hence the molecule becomes distorted pentagonal bipyramidal as shown in figure 3.39.
XeF6 molecule: In this molecule, Xenon exhibits sp3d3 hybridization and forms seven equivalent hybrid orbitals in which only one hybrid orbital is fully-tilled and the remaining six hybrid orbitals are half-filled. These half-filled sp3d3hybrid orbitals of xenon-atom overlap with six hail-filled 2pz-atomic orbitals of six F-atoms to form the XeF6 molecule. Thus, XeF6 has a pentagonal bipyramidal structure with an l.p. at the axial position. This is possible only when Xe-atom in XeF6 molecule is in a triply excited state as shown below: