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🌟🔷 Atomic Orbital Hybridization (AOH) | Shapes, Bonds & Smart Tricks for Students
intermixing
The intermixing or hybridization of atomic orbitals is a mathematical concept based on quantum mechanics. During this process, the wave functions, Ψ (psi) of atomic orbitals of same atom are combined to give new wave functions corresponding to hybrid orbitals.
Definition of Hybridization
In order to account for equivalent Valecny of elements (i.e. tetravalency of carbon, trivalency of group III A elements, divalency of group II A elements), identical bonds formation by group IVA (C), IIIA (B) and IIA (Be) elements and to explain bond angles in H₂O and NH₃ molecules, Linus Pauling (Nobel laureate) introduced the concept of hybrid orbitals and hybridization in 1931.
The process of hybridization is a hypothetical process and for an isolated atom hybridization
has no meaning. The concept of hybridization is an extension of atomic orbital theory (AOT) or valence bond theory (VBT).
The word hybridization means mixing or blending. The process of blending or mixing of different pure atomic orbitals of the same atom having slightly different energies to produce a set of same number of new equivalent degenerate orbitals of identical energy, size and shape called hybrid orbitals which are equal in number to the mixing orbitals having specific spatial orientation in space round the atom is termed as atomic orbital hybridization and the new equivalent blended or modified atomic orbitals formed having same energy, size and shape possessing specific geometry are called hybrid orbitals.
Hybrid orbitals are also atomic orbitals but are not pure atomic orbitals and are regarded as modified or blended atomic orbitals. The number of Hybridized orbitals produced is equal to the number of hybridizing atomic orbitals (which are being hybridized). The hybrid orbitals are designated according to the number of mixing atomic orbitals.
Hybridization is the process of reorganization (redistribution) or intermixing of two or more half-filled, fully-filled, incompletely-filled or empty pure atomic orbitals of an atom with almost same energy or slightly different energies (like “s’ and “p” orbitals) thereby forming same number of new equivalent or identical and degenerate orbitals having equivalent energies and shapes. The new orbitals formed are also known as hybrid orbitals.
For example, one 2s-orbital hybridizes with two 2p-orbitals of carbon to form three new sp2-hybrid orbitals. These hybrid orbitals have minimum repulsion between their electron pairs and thus, are more stable.
Hybridization is of six types i.e. sp, sp² and sp³ sp³d, sp³d², sp³d³ hybridization. Each type of hybridization has a specific geometry.
Analogy
for Atomic Orbital Hybridization
1. Mixing of a pure
s-orbital and one or more p-orbitals is rather like mixing of a gallon of pure
red paint and one or more gallons of white
paint to give two or more
gallons of new pink
coloured paint.
2. Two liquids, one blue and one yellow, are
combined to form one green solution as an analogy for hybrid orbitals.
3. A Pop Analogy: Hybrid Soda
A little analogy that might help to explain hybrid orbital and
hybridization.
Imagine you have four bottles of pop:
one bottle of Sprite (S) and three bottles of Pepsi (P).
Now imagine pouring them out, mixing
them all together, and then re-filling each bottle with the mixture.
The Law of Conservation of Pop says
that you still have four bottles worth of liquid. But now the pop is neither
pure Sprite or pure Pepsi; it is a hybrid between the two.
Specifically, each bottle now has 25%
Sprite character and 75% Pepsi character.
We can call this “hybrid” pop, analogous
to sp³ hybrid orbitals.
Hybrid
Orbitals
the new equivalent blended or modified atomic orbitals formed by the intermixing of pure or standard atomic orbitals having same energy, size and shape possessing specific geometry are called hybrid orbitals. Hybrid orbitals are also atomic orbitals but are not pure atomic orbitals and are regarded as modified or blended atomic orbitals.
The number of Hybridized orbitals
produced is equal to the number of hybridizing atomic orbitals (which are being
hybridized). For example, one 2s-orbital hybridizes with two 2p-orbitals
of carbon to form three new sp²-hybrid orbitals. These hybrid orbitals
have minimum repulsion between their electron pairs and thus, are more stable.
Hybrid orbitals are directional (unlike s-orbital) and have lower energy than
parent atomic orbitals.
During hybridization, the hybrid orbitals possess different geometry of orbital arrangement and energies than the standard atomic orbitals. Also, the orbital overlap minimizes the energy of the molecule. The degenerate hybrid orbitals formed from the standard atomic orbitals:
One s and One p: Two sp orbitalsOne s and Two p: Three sp² orbitals
One s and Three p: Four sp³ orbitals
One s, Three p, and one d: Five sp³d orbitals
One s, Three p, and two d: Six sp³d² orbitals
One s, Three p, and three d: Seven sp³d³ orbitals
Hybrid orbitals are not real. Hybrid orbital with less s-% is less spherical while with more s-% is more spherical.
As the bond angle increases, p-character
decreases and vice-versa
In H2O, bond angle is 104° instead of 109.28°, that means angle decrease hence p-character will increase hence p% = 80, now s% = 20 i.e. sp3 hybridization.
Unhybrid
Orbitals
The atomic orbitals which are not involved in intermixing retaining their shapes lying perpendicularly to the hybrid orbitals are termed as unhybrid orbitals.
Significance of Hybridization
1. The concept of atomic orbital hybridization gives a satisfactory explanation for the equivalent valencies of the polyvalent elements.
2. It holds significant importance in determining the nature of bonds and shape (geometry) of the polyatomic molecules.
Conditions or Requirements for Hybridization
1. The orbitals present
in the valence shell of same atom take part in hybridization.
(The hybridization is the mixing of orbitals of same atom only. The combination of orbitals belonging to different atoms is called bonding).
2. Hybridizing orbitals should have almost same or slight (small) difference in their energies i.e. the orbitals undergoing hybridization should have almost equal energy.
3. Only the orbitals and not the electrons get hybridized.
4. The fully-filled or half-filled or even empty orbitals can undergo hybridization provided they have almost equal energy.
5. Promotion of electron is not essential condition prior to hybridization.
Types of Hybridization Based on
Nature of participating orbitals
1. sp-hybridization (AB₂
molecules, beryllium chloride, acetylene, CO₂, CS₂ etc.)
2. sp²-hybridization (AB₃
molecules, boron trichloride, ethylene, benzene, etc.)
3. sp³-hybridization(AB₄ molecules, methane, ethane)
4. sp³d-hybridization (AB₅ molecules, phosphorus
pentachloride)
5. sp³d²-hybridization (AB₆ molecules, sulphur hexafluoride)
6. sp³d³-hybridization (AB₇ molecules, iodine heptafluoride)
How to determine Type of
Hybridization
H
= ½ (V + M + A – C)
Where
H =
No of HO involved viz 2, 3,4,5,6,7, hence nature of hybridization will be sp,
sp2,sp3, sp3d, sp3d2, sp3d3
V = No of electrons in valence shell of the
central atom
M= Number of monovalent atom
A = Charge on cation
C = Charge
on anion
Characteristics of Hybrid Orbitals
1.
Equivalent and Degenerate Orbitals
The hybrid orbitals are of equivalent shape, size and energy. The hybrid orbitals are degenerate i.e. they are associated with same energy. The shapes of hybrid orbitals are identical. Usually they have one big lobe associated with a small lobe on the other side.
2.
Number of Hybrid Orbitals equals to number of hybridizing orbitals
The number
of hybrid orbitals produced is equal to the number of hybridizing orbitals.
e.g. If 3 atomic orbitals intermix with each other, the number of hybrid orbitals formed will be equal to 3.
3.
Atomic in nature/Blended orbitals
Hybrid orbitals are also atomic orbitals.
4.
Intermediate Characteristic of parent atomic orbitals
They show properties and energies intermediate between those of parent atomic orbitals i.e. they have mixed characteristics of parent atomic orbitals.
5.
Three-dimensional orientation at maximum possible distance
Hybrid orbitals are orientated at maximum possible distance three dimensionally.
6.
Prediction of molecular geometry by Hybrid orbitals
Hybridized orbitals can rationalize the geometry of molecules. i.e. the type of hybridization indicates the geometry of molecules.
7.
Formation of stronger bonds
Hybridized bonds can make stronger bonds than pure AO with other atoms like hydrogen.
8.
Formation of only one sigma bond
Hybrid orbitals form only sigma bonds.
9.
Occurrence in bonded atom of molecule
Hybridization never takes place in an isolated atom but it occurs only at the time of bond formation i.e. it occurs in the central bonded atom in a molecule.
10.
Number of hybrid orbitals must be equal to the oxidation state of the central
atom
In the excited state, the number of unpaired electrons must correspond to the oxidation state of the central atom of the molecule.
11. Sign of lobes of the Hybrid
orbital
The bigger lobe of the hybrid orbital always has a positive sign, while the smaller lobe on the opposite side has a negative sign.
Among sp, sp² and sp³, which hybrid
orbital is more electronegative?
The percentage of s character in sp, sp², and sp³ hybridized carbon is 50%, 33.33%, and 25%, respectively. Due to the spherical shape of s orbital, it is attracted evenly by the nucleus from all directions. Therefore, a hybrid orbital with more s-character will be closer to the nucleus and thus more electronegative. Hence, the sp hybridized carbon is more electronegative than sp² and sp³.
Why is the hybrid orbital during
hybridization better than their parent atoms?
The reason why a hybrid orbital is
better than their parents:
Parent s: because it is directional
unlike the s-orbital.
Parent p: because it has lower energy than p-orbital.
Amide
molecule looks sp³ hybridized but it is sp², why?
The general
process of hybridization will change if the atom is either enclosed by two or
more p orbitals or it has a lone pair to jump into a p orbital. Therefore, in
the case of amide molecule, the lone pair goes into a p orbital to have 3
adjacent parallel p orbitals (conjugation).
Summary of 6 Types of Hybridization
Difference Between sp3, sp2 and sp hybridization
Explanation of orbital hybridization with special reference to Beryllium, Boron and Carbon
Ground State Configuration
The number of half-filled valence orbitals or unpaired electrons in the valence shell of an atom constitutes its valency. However, this rule is violated in compounds of group IIA (Be), IIIA (B) and IVA (C) etc.
from their ground or atomic states electronic configuration in terms of unpaired electrons, Be appear to behave as an inert gas (valency = 0), boron might be expected to be monovalent (valency =1) and carbon would be divalent (valency = 2) due to the presence of one, two and three half-filled orbitals respectively. In actual practice, however, Be, B and C are divalent, trivalent and tetravalent in most of its compounds respectively.
Excited State Configuration
To account for these discrepancies (anomalies) in the valency of such elements, it is assumed that some of the paired electrons are uncoupled and one of the electron from the lower energy orbital belonging to the ground state (2s) is promoted to empty orbital of slightly higher energy (py and pz) before bond formation achieving the excited state. This arrangement of electrons after promotion is referred to as an excited state. The excited state electronic configuration results in an increase in the number of unpaired electrons.
The promotion will require an input of energy. The energy required for the excitation (promotion) and unpairing the electron (of 2s) is compensated by the heat of reaction (energy) released during hybridization and the process of additional covalent bond formation. According to these excited state electronic configurations, Be becomes divalent, boron becomes trivalent while carbon becomes tetravalent.
Hybridized State
On the basis of excited state electronic configuration, it might be expected that Be would form 2 covalent bonds, boron would form 3 and carbon would form 4 covalent bonds. One expect that in CH₄, three C–H bonds formed by the overlap of three 2p–orbitals would be identical (having directional nature and higher energy) while the fourth C–H bond formed due to 2s-orbtial would be different (having non-directional nature and lower energy). In actual practice, all four C–H bonds in CH4 are identical in all respects (i.e. in bond energy and bond length).
Linus Pauling settled this disparity by suggesting the idea of hybridization involving the mixing of atomic orbitals having nearly equal energies in various ways within an atom to form equivalent hybrid orbitals. It means that atomic orbitals of Be, B and C have equalized their energies, size and shape. This process is called Hybridization and these atoms are said to be HYBRIDIZED.
Ground State, Excited State and Hybridized State EC of Be, B and C
sp³-Hybridization (Tetrahedral or Tetragonal Hybridization)
Definition
In this type of hybridization, ‘s’ and p-orbitals of the valence shell of the central atom of the given molecule intermix with each other in the ratio of 1:3 to form four sp3-hybrid orbitals.
The type of hybridization involving combination of one “s” (2s) and three “p” (2p) atomic orbitals to produce four new equivalent “sp³” hybrid orbitals which are arranged tetrahedrally with bond angle 109.5° is called sp³ Hybridization or tetrahedral hybridization.
The hybrid orbitals are different than the pure s or p orbitals having
the character of both s and p orbitals in the ratio of 1:3. These sp³ hybrid orbitals are directed towards the four corners of
regular tetrahedron in which each angle is 109.5°.
Energy Level Diagram for sp³
Hybridization
Occurrence of sp³-hybridization
sp³ hybridization is found in those
compounds where central atom (carbon) is bonded by
other 4 atoms or groups i.e. AB₄ molecules like CH₄, CCl₄, CBr₄, SiCl₄, SiH₄, SnCl₄,
Characteristics sp³ Hybrid Orbital
Identical in All aspects
All the four sp3 hybrid orbitals are completely equivalent and symmetrical.
Mixed s and p-character in 1:3 ratio
Each sp3 hybrid orbital has 25% s-character and 75% p character (1:3).
No of electrons in Hybrid orbital
Each sp3 hybrid orbital has 1 electron.
Spatial Orientation is tetrahedral/ tetrahedral Geometry of sp³ hybrid orbitals
sp³-hybrid orbitals are directed towards the four corners of regular tetrahedron in which each angle is 109.28°(or 109.5°). sp³-hybrid orbitals are directed towards the four comers of a regular tetrahedron and the angle between each pair of them is 109°28' (or 109.5°). sp³-hybrid orbitals are four in number, which are arranged tetrahedrally with carbon located at the center. Angle between two sp³-hybrid orbital is 109.5° (109.28°).
Greater
Relative Power of overlapping of
2.00
Their relative power of overlapping is 2.00 with respect to s-orbital. This shows that sp3-orbitals are stronger than sp² which is stronger than sp-orbitals.
Shape of sp³
Hybrid Orbital
Since in sp³-hybridisation the
contribution of p-orbitals is 75%, its shape is almost same as that of the
parent p-orbitals except that the bigger lobe in sp3-orbital is
somewhat more spread and shorter in length than the pure p-orbitals.
Hybrid Molecular Structure of Methane (Detailed Description of Shape of Methane)
In methane i.e. CH₄, carbon is bonded to four hydrogen atoms, thus carbon gets sp³-hybridized and uses sp³ hybrid orbitals to make its bonds.
(The sp³
hybridization in C of CH₄ can be proved by considering its electronic
configuration in different states. The ground state electronic configuration of
carbon is 1s↿⇂ 2s↿⇂ 2pₓ↿ 2pᵧ↿ 2p𝓏⁰ showing that it is divalent. But it is
assumed that one electron from 2s orbital get promoted to 2pz orbital to make
it tetravalent resulting in its excited state electronic configuration of
carbon is 1s↿⇂ 2s↿ 2pₓ↿ 2pᵧ↿ 2p𝓏↿. These four half-filled orbitals of carbon (one s and three p orbitals) undergoes
mixing to produce four new equivalent sp³ hybrid orbitals of equal energy and
shape directed towards the corner of a regular tetrahedron at angle of 109.5°
assuming a tetrahedral structure.).
There are
four sigma bonds in CH₄. Each sp³ hybrid orbital with one electrons overlaps
with 1s orbital of H atom on linear axis to form four C–H sigma bonds. (Each
H–C bond is a sigma bond which is formed due to s-sp³ overlapping. Thus CH₄ has
tetrahedral geometry. Each bond angle in CH₄ is 109.28° (109.5°). The bond
length between C–H is 1.09Å.
Brief
Description Hybrid Molecular Structure or Shape of Methane
Hybrid Molecular Structure of Ammonia (NH₃)
In ammonia i.e. NH₃, nitrogen is bonded to three hydrogen atoms with one lone pair on N atom, thus nitrogen gets sp³-hybridized and uses sp³ hybrid orbitals to make its bonds.
(The sp³
hybridization in N of NH₃ can be proved by considering its electronic
configuration in different states. The ground state electronic configuration of
nitrogen is 1s↿⇂ 2s↿⇂ 2pₓ↿ 2pᵧ↿ 2p𝓏↿. But
it is assumed that one electron from 2s orbital get promoted to 2pz orbital
resulting in its excited state electronic configuration of nitrogen is 1s↿⇂ 2s↿ 2pₓ↿ 2pᵧ↿ 2p𝓏↿⇂. These three half-filled and
one fully filled orbitals of valence shell of nitrogen undergoes
mixing to produce four new equivalent sp³ hybrid orbitals of equal energy and
shape directed towards the corner of a regular tetrahedron at angle of 109.5°.
Ground State electronic configuration of 7N = 1s↿⇂ 2s↿⇂ 2px↿ 2py↿ 2pz↿
Excited State electronic configuration of 7N* = 1s↿⇂ 2s↿ 2px↿ 2py↿ 2pz↿⇂
Hybridized state electronic configuration of 7N = 2s↿ + 2px↿ + 2py↿ + 2pz↿⇂ Þ sp₃↿ + sp₃↿
+ sp₃↿ + sp₃↿⇂
Out of four sp3 hybrid orbitals of nitrogen, three have single electrons which overlap with 1s orbital of 3 hydrogen atoms to form three N–H sigma bonds. The fourth non-bonding sp3 orbital with one lone pair on nitrogen remains unbounded.
Because the
repulsion of lone pair is greater than bond pairs, the shape of ammonia
molecule is not regular tetrahedron. The stronger repulsion of non-bonding
orbital on N deviates the bond angle from 109.5° to 107°. The distortion of
bond gives rise to pyramidal geometry in ammonia molecule.
The H–N–H
bond angle in NH3 (107°) is less than the normal tetrahedral angle
(109°.28). This is due to:
(i)Lone
pair-bond pair repulsion is greater than bond pair-bond pair repulsion. As a
result, bond pairs move away from the lone pair and come closer to each other,
which result in reduction of bond angle.
(ii)The
non-bonding orbitals occupies large volume, hence they compress bonding orbital
and reduces bond angle.
Brief
Description Hybrid Molecular Structure or Shape of Ammonia (NH3)
predicted by Hybrid Orbital Model
Hybrid
Molecular Structure of Water (H₂O)
In water i.e. H₂O, oxygen is bonded to two hydrogen atoms with two lone pair on O atom, thus oxygen gets sp³-hybridized in H₂O and uses sp³ hybrid orbitals to make its bonds.
This can be
explained by considering its electronic configuration:
The ground state electronic configuration of oxygen is 1s↿⇂ 2s↿⇂ 2pₓ↿ 2pᵧ↿ 2pz↿⇂. But it is assumed that one electron from 2s orbital get promoted to 2pᵧ orbital resulting in its excited state electronic configuration of oxygen is 1s↿⇂ 2s↿ 2pₓ↿ 2pᵧ↿⇂ 2pz↿⇂. These two half-filled and two fully filled orbitals of valence shell of oxygen undergoes mixing to produce four new equivalent sp³ hybrid orbitals of equal energy and shape directed towards the corner of a regular tetrahedron at angle of 109.5°.
Ground State electronic configuration of ₈O = 1s↿⇂ 2s↿⇂ 2px↿ 2py↿ 2pz↿⇂
Excited State electronic configuration of ₈O* = 1s↿⇂ 2s↿ 2px↿ 2py↿⇂ 2pz↿⇂
Hybridized state electronic configuration of ₈O = 2s↿ + 2px↿ + 2py↿⇂ + 2pz↿⇂ Þ sp↿3 +sp↿3 + sp↿⇂ 3 + sp↿⇂ 3
Out of four
sp³ hybrid orbitals of oxygen, two have single electrons which overlap with 1s
orbital of hydrogen atoms to form two O–H sigma bonds. The remaining two
non-bonding sp³ orbitals with two lone pairs on oxygen remains unbounded.
Because the repulsion of lone pair is grater than bond pairs, the shape of water
molecule is not regular tetrahedron. The stronger repulsion of non-bonding
orbital on O deviates the bond angle from 109.5° to 104.5°. The distortion of
bond gives rise to angular geometry in water molecule.
[1s orbital
of hydrogen atom overlaps two sp³ hybrid orbitals to give two sigma bonds with
two non-bonding orbitals on oxygen. The H–O–H bond angle in H₂O (104°.5) is
less than the normal tetrahedral angle (109°.5)].
The bond
angle is less than the normal tetrahedral angle (109°.5) due to following
reasons:
(i) Lone
pair-bond pair repulsion is greater than bond pair-bond pair repulsion causing bond
pairs move away from the lone pair and come closer to each other which result
in reduction of bond angle.
(ii) The non-bonding
orbitals occupies large volume, hence they compress bonding orbital and reduces bond angle.
Brief
Description Hybrid Molecular Structure or Shape of Water (H2O)
predicted by Hybrid Orbital Model
