Atomic Orbital Hybridization (AOH)

 

Atomic Orbital Hybridization (AOH)

 

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 an atom differing slightly in energy to produce a set 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

Mixing of a pure s-orbital and one or more p-orbitals is rather like mixing of a gallon of pure red pain and one or more gallons of white paint to give two or more gallons of new pink coloured paint.

Two liquids, one blue and one yellow, are combined to form one green solution as an analogy for 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 orbitals

One 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^o instead of 109.28^o, that means angle decrease hence p-character will increase hence p% = 80, now s% = 20 i.e. sp⁴ 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.

Difference between Hybrid orbitals and 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        (beryllium chloride, acetylene)

2. sp²-hybridization      (boron trichloride, ethylene)                       

3. sp³-hybridization      (methane, ethane)                       

4. sp³d-hybridization    (phosphorus pentachloride)

5.  sp³d²-hybridization   (sulphur hexafluoride)

6. sp³d³-hybridization   (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. 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.  The number of hybrid orbitals produced is equal to the number of hybridizing orbitals. e.g. If three atomic orbitals intermix with each other, the number of hybrid orbitals formed will be equal to 3.

 

3. Hybrid orbitals are also atomic orbitals.

 

4.  They show properties and energies intermediate between those of parent atomic orbitals i.e. they have mixed characteristics of parent atomic orbitals.

 

5. Hybrid orbitals are orientated at maximum possible distance three dimensionally.

 

6. Hybridized orbitals can rationalize the geometry of molecules. i.e. the type of hybridization indicates the geometry of molecules.

 

7.         Hybridized bonds can make stronger bonds than pure AO with other atoms like hydrogen.

 

8.         Hybrid orbitals form only sigma bonds.

 

9.  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. In the excited state, the number of unpaired electrons must correspond to the oxidation state of the   central atom of the molecule.

 

11.       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

 

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 angel is 109.5°.

 

Energy Level Diagram

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, NH₄⁺, PH₄⁺, SO₄^2-, ClO₄^2-, CrO₄^2- etc. It is the characteristic of saturated hydrocarbons in which carbon is bonded to four hydrogen atoms or 4 other atoms e.g. Alkane i.e. Methane (CH₄), Ethane (C₂H₆) etc.

 

Characteristics

Each sp³ hybrid orbital has 25% s-character and 75% p character (1:3).

 

Geometry

sp³-hybrid orbitals are directed towards the four corners of regular tetrahedron in which each angle is 109.28°.

 

Character

 

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 hybridized 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

These 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 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^↿⇂ 2p_x^↿ 2p_y^↿ 2p_z⁰ 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^↿ 2p_x^↿ 2p_y^↿ 2p_z^↿. 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.).

 

Ground State electronic configuration of ₆C  = 1s^↿⇂ 2s^↿⇂ 2p_x^↿ 2p_y^↿ 2p_z

Excited State electronic configuration of ₆C ^* = 1s^↿⇂ 2s^↿ 2p_x^↿ 2p_y^↿ 2p_z^↿          

Hybridized state electronic configuration of ₆C  = 2s^↿ + 2p_x^↿ + 2p_y^↿ + 2p_z^↿⇂  Þ sp^↿3 +sp^↿3 + sp^↿3 + sp^↿3

 

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 1.09°A.

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^↿⇂ 2p_x^↿ 2p_y^↿ 2p_z^↿. 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^↿ 2p_x^↿ 2p_y^↿ 2p_z^↿⇂. 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^↿⇂ 2p_x^↿ 2p_y^↿ 2p_z^↿          

Excited State electronic configuration of ₇N^* = 1s^↿⇂ 2s^↿ 2p_x^↿ 2p_y^↿ 2p_z^↿⇂         

Hybridized state electronic configuration of ₇N  = 2s^↿ + 2p_x^↿ + 2p_y^↿ + 2p_z^↿⇂  Þ sp^↿3 + sp^↿3 + sp^{↿ 3} + sp^{↿⇂ 3}

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.

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^↿⇂ 2p_x^↿ 2p_y^↿ 2p_z^↿. But it is assumed that one electron from 2s orbital get promoted to 2pz orbital resulting in its excited state electronic configuration of oxygen is 1s^↿⇂ 2s^↿ 2p_x^↿ 2p_y^↿ 2p_z^↿⇂. 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^↿⇂ 2p_x^↿ 2p_y^↿ 2p_z^↿⇂         

Excited State electronic configuration of ₈O^* = 1s^↿⇂ 2s^↿ 2p_x^↿ 2p_y^↿ 2p_z^↿⇂         

Hybridized state electronic configuration of ₈O  = 2s^↿ + 2p_x^↿ + 2p_y^↿ + 2p_z^↿⇂  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. 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.

sp²-Hybridization (Trigonal Hybridization)

 

Definition

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 1:2 to form three sp²-hybrid orbitals.

 

The type of hybridization involving combination of one ‘s’ (2s) and two ‘p’ (2p) atomic orbitals to produce three new equivalent sp² Hybrid Orbitals of same shape and energy which are arranged trigonally with bond angle of 120° is called sp² hybridization.

 

The third 2p or 2p_z orbital (if present) remains unhybridized lie at right angle (90°) to the plane of sp² hybrid orbitals.

 

Energy Level Diagram    

Occurrence of sp²-Hybridization

sp² Hybridization is found in those compounds where central atom (carbon) is bonded by other three atoms or groups i.e. AB₃ molecules like BF₃, BCl₃ etc. It is the characteristic of unsaturated hydrocarbons in which carbon is bonded to three other atoms e.g. Alkene i.e. ethene (C₂H₄), C₆H₆ (Benzene) etc.

 

Characteristics

Each sp² hybrid orbital has 33.3% s-character and 66.7% p-character (1:2).

 

Geometry

sp²-hybrid orbitals are coplanar and directed towards the three corners of equilateral triangle in which each angle is 120°.

Character

 

Identical in All aspects

These sp²-hybrid orbitals are completely equivalent and symmetrical.

 

Mixed s and p-character in 1:2 ratio

Each sp² hybrid orbital has 33.33% (one third) s-character and 66.66% (two third) p-character (1:2).

 

No of electrons in Hybrid orbital

Each sp² hybrid orbital has 1 electron.

 

Spatial Orientation is trigonal

sp² hybrid orbitals are three in number and are co-planar which are trigonally place (i.e. they lie in the same plane with their axes directed towards the corners of a regular triangle) and they directed towards the corners of an equilateral triangle (trigonal) at an angle of 120° to each other. The fourth p atomic orbital which is not involved in hybridization remains un-hybridized at right angle to the plane of hybridized sp² orbitals.

 

Shape of Hybrid Orbital

Since in this hybridization contribution of p-orbitals is more hence it is less oval than sp-hybrid orbitals. In this case one lobe is bigger and one lobe is smaller and it forms stronger bond.

 

Moderate Relative Power of overlapping of 1.99

These are stronger than s and p orbitals. Its relative power of overlapping is 1.99 with respect to s-orbital.

Hybrid Molecular Structure of Ethene; C₂H₄ (Ethylene)

Ethene molecules consists of two central carbon atoms. In ethene i.e. C₂H₄, each carbon is bonded to three other atoms (i.e. 2 H and 1 C atom) thus each carbon uses sp² hybrid orbitals plus unhybrid p_z orbital to make its bonds.

 

The three sp² hybrid orbitals arrange themselves in trigonal planar geometry at 120°. One sp²-hybrid orbital of each carbon atom overlaps linearly with other carbon to form a C–C sigma bond. The remaining two sp²-hybrid orbitals of each carbon overlaps linearly with 1s orbitals of two hydrogen atoms to form four C–H sigma bonds. Now unhybrid p_z orbitals of both carbon atoms which lie at right angle overlap side wise to form a pi bond between carbon to carbon.

 

There are five sigma bonds in C₂H₄, 4 in between C and H and one in between C and C, while one Pi bond in between C and C. Thus C₂H₄ has trigonal geometry. All bond angles (H-C-H and H-C-C) are 120°. Each C-H bond length is 1.09°A and each C=C bond length is 1.34°A (shorter than C-C bond length in CH₃-CH₃ which is 1.54°A).

Summary of Shape of Ethene predicted by Hybrid orbital model

 

Planar Trigonal Shape of BF₃ predicted by Hybrid Orbital Model

Since in BF₃, boron (central atom) is attached with three F atoms, thus according to hybridization, Boron uses its sp² hybrid orbitals to make its bonds i.e. in BF₃, Boron is sp² hybridized.

 

This can be proved by considering its ground state, excited state and hybridized electronic configurations:

These three half-filled orbitals of boron (one s and two p orbitals) undergoes mixing to produce three new equivalent sp² hybrid orbitals of equal energy and shape lying in the same plane (coplanar) directed towards the corners of an equilateral triangle (trigonal) at an angle of 120° to each other making planar triangular geometry.

 

These three sp² orbitals of boron overlap with 2p_z orbital of three fluorine atoms to give three B–F  sigma bonds. Thus BF₃ molecule acquires Planar Trigonal Structure.

 

sp-Hybridization (Diagonal 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 1:1 to form two sp-hybrid orbitals.

 

The type of hybridization involving combination of one s (2s) and one p (2p) atomic orbitals of the valence shell of the central atom of the given molecule to produce two new equivalent sp-hybrid orbitals of identical shape and energy which are arranged co-linearly with a bond angle of 180^○ is called sp-hybridization.

 

The two 2p or 2p_y and 2p_z orbitals (if present) remain unhybridized which lie at right angle (90°) to the plane of sp-hybrid orbitals.

Energy Level Diagram

Occurrence of sp-Hybridization

sp-Hybridization is found in those compounds where central atom (carbon) is bonded by other two atoms or groups i.e. AB₂ molecules like BeCl₂, CO₂, CS₂ etc.. It is the characteristic of unsaturated hydrocarbons in which carbon is bonded to two hydrogen atoms e.g. Alkyne i.e. ethyne (C₂H₂),

 

Characteristics

Each sp^-hybrid orbital has 50% s-character and 50% p character (1:1).

 

Geometry

sp-hybrid orbitals co-axial or co-linear i.e. they lie at the same straight line in which each angle is 180^○.

Characters

Identical in All aspects

Both sp-hybrid orbitals are completely equivalent and symmetrical.

 

Mixed s and p-character in 1:1 ratio

Each sp hybrid orbital has 50% s-character and 50% p-character (1:1 ratio). Energy of sp-hybrid orbital is more than s-orbital but less than the p-orbital.

 

No of electrons in Hybrid orbital

Each sp hybrid orbital has 1 electron.

 

Spatial Orientation is Co-linear  

The sp hybrid orbitals are co-axial or co-linear at an angle of 180° (i.e. they lie at the same straight line) which provide maximum separation and overlap. The unhybridized p (2p_y and 2p_z) orbital is at the right angles to each other and to the plane of hybrid orbitals. Angle between two sp-hybrid orbitals is 180^○.

 

Least Relative Power of overlapping of 1.99

Its relative power of overlapping is 1.93 with respect to s-orbital.

 

Shape of Hybrid Orbital

Shape of sp-hybrid orbital is oval. In sp-hybrid orbital one lobe is bigger while other lobe is small. The bigger lobe is very large with respect to p-orbital, hence it has higher degree of overlapping. Thus it forms stronger bond.

 

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.

Shape of Beryllium Chloride (BeCl₂) predicted by Hybrid Orbital Model

Since in BeCl₂, beryllium (central atom) is attached with two Cl atoms, thus according to hybridization, Be uses its sp hybrid orbitals to make its bonds i.e. in BeCl₂, Beryllium is sp hybridized.

 

This can be proved by considering its ground state, excited state and hybridized electronic configurations:

These two half-filled orbitals of beryllium (one s and one p orbital) undergoes mixing to produce two new equivalent sp hybrid orbitals of equal energy and are co-linear at an angle of 180° which provide maximum separation and overlap making linear geometry.

 

These two sp hybrid orbitals of beryllium overlap with 3p_z orbital of two chlorine atoms in straight line to give two Be–Cl sigma bonds. Thus BeCl₂ molecule acquires linear structure. The linear geometry of molecule is due to the maximum repulsion of two electron pairs. 

Hybrid Molecular Structure of Ethyne (Acetylene)

In ethyne (acetylene), each carbon is bonded to two atoms (i.e. one H atom and one C atom) thus each carbon uses sp hybrid orbitals plus two unhybrid p_y and p_z orbitals to make its bonds.

 

In sp hybridization of each carbon in ethyne there is a mixing of only s and p_x orbitals to give two sp hybrid orbitals that arrange linearly  at 180° angles while the two unhybrid orbitals p_y and p_z are inclined at right angle to the sp hybrid orbitals as well as to each other. The two hybrid sp orbitals and the two unhybrid atomic orbitals p_y and p_z contain single electron.

 

One sp-hybrid orbital of each carbon atom overlaps linearly with sp orbital of other carbon to form a C-C sigma bond. The remaining sp-hybrid orbital of each carbon overlap with 1s orbital of Hydrogen atoms to form two C–H sigma bonds. Thus overall three sigma bonds are formed at 180^○ angles which makes linear geometry.

 

Two unhybrid atomic orbitals (2p_y and 2p_z) of each carbon lying parallel to each other undergoes side wise overlapping to form two pi bonds between C to C. One sigma and two pi bonds between the carbon atoms of ethyne molecules is termed as triple bond.

 

All bond angles (H–C–C) is 180^○. Each C–H bond length is 1.09^○A and each C–C bond length is 1.2^○A (which is shorter than C-C and C=C bond lengths).