B.sc 1st year Book (Page 13)
Hybridization of atomic orbitals
Case of Hybridization :
Why do the hybrid orbitals form Stronger bonds?
Conditions for 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
|Chemical Bonding||Inert Pair Effect|
|Lattice energy||Fajans Rule|
|Covalent Bond||Coordinate Bond|
|Odd electron bond||Metallic bond|
|Hydrogen Bonding||M.O. Theory|
|Sidgwick-Powell theory||VSEPR theory|
|Hybridization of atomic orbitals|
Types of hybridization :
1- sp hybridization or linear hybridization:
Characteristics of sp-hybrid orbitals :
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 :
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 :
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 :
3- sp3 hybridization or Tetrahedral hybridization:
Characteristics of sp3 hybrid orbitals :
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 :
CH4 molecule :
Type of molecules and ions which undergo sp3 hybridizations:
(a) AB type of molecules :
(b) AB2 type of molecules or Ions:
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:
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 :
Thus, the structure of ammonium ion, NH4+ion is tetrahedral.
dsp² Hybridization :
This d-orbital with one s and two p-orbitals forms four ds2 hybrid orbitals.
dsp3 or sp3d Hybridization or Trigonal-bipyramidal hybridization:
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.
(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 :
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:
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.
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:
AB2 type of molecules or ions :
Since the throe Ip’s occupy three basal hybrid orbitals and do not involve in overlapping hence the shape of the molecule is linear.
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 :
Characteristics of sp3d2 hybrid orbitals :
(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 :
AB6 type of molecules or ions or Regular octahedral species :
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.
AB5 type of molecules or ions/or Square pyramidal species :
In the AB5 molecule, atom A is the central atom. Lewis structure of this molecule is –
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 :
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.
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.
(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) 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.
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.