Difference Between sp sp2 and sp3 Hybridization

Main Difference – sp vs sp² vs sp³ Hybridization

Orbitals are hypothetical structures that can be filled with electrons. According to different discoveries, scientists have proposed different shapes for these orbitals. There are three main types of orbitals: atomic orbitals, molecular orbitals, and hybrid orbitals. Atomic orbitals of an atom undergo hybridization to make suitable orbitals for chemical bonding. In chemistry, hybridization is the mixing of different atomic orbitals to form hybrid orbitals. There are different forms of hybridizations which make different forms of hybrid orbitals such as sp, sp² and sp³ hybrid orbitals. These orbitals are formed by the hybridization of s and p atomic orbitals in different ratios. The main difference between sp sp² and sp³ hybridization is that sp hybridization forms hybrid orbitals having 50% s orbital characteristics and sp² hybridization forms hybrid orbitals having 33% s orbital characteristics whereas sp³ hybridization forms hybrid orbitals having 25% s orbital characteristics.

Key Areas Covered

1. What is sp Hybridization
     – Definition, Calculation of S and P Characteristics, Other Features
2. What is sp² Hybridization
     – Definition, Calculation of S and P Characteristics, Other Features
3. What is sp³ Hybridization
     – Definition, Calculation of S and P Characteristics, Other Features
4. What is the Difference Between sp sp² and sp³ Hybridization
     – Comparison of Key Differences

Key Terms: Atomic Orbital, Hybrid Orbitals, Hybridization, Orbitals, Sp Hybridization, Sp² Hybridization, Sp³ Hybridization

What is sp Hybridization

sp hybridization is the hybridization that takes place between an s atomic orbital and a p atomic orbital. An electron shell contains three p orbitals. Therefore, after the hybridization of an s orbital with one of these p orbitals, there are two un-hybridized p orbitals present in that atom. Here, we consider that all s and p orbitals as just atomic orbitals (s+p). The ratio between s and p orbitals is 1:1. Therefore the fraction of s orbital is 1/2, and the fraction of p orbitals is 1/2.

S (or p) characteristic percentage = total atomic orbitals  x  (1/2)  x  100%
                                                              = 50%

Figure 1: sp Hybridization

The resulting hybrid orbitals have 50% of s characteristics and 50% of p characteristics. Since only two hybrid orbitals formed, the spatial arrangement of sp orbitals is linear. The two hybrid orbitals are directed to opposite directions. Hence, the angle between these orbitals is 180^oC.

What is sp² Hybridization

sp² hybridization is the mixing of one s atomic orbital with two p atomic orbitals. The newly formed hybrid orbitals are known as sp² hybrid orbitals. The resulting hybrid orbitals have about 33.33% of s characters and about 66.66% of p characters. This is because a total of three atomic orbitals are involved in the hybridization, and the percentages of s and p characteristics vary as follows.

Here, we consider that all s and p orbitals as just atomic orbitals (s+p+p). The ratio between s and p orbitals is 1:2. Therefore the fraction of s orbital is 1/3 and the fraction of p orbitals is 2/3. 

S characteristic percentage = total atomic orbitals  x  (1/ 3)  x  100%
                                                  = 33.33 %
P characteristic percentage = total atomic orbitals  x  (2/ 3)  x  100%
                                                  = 66.66 %

Figure 2: sp² Hybridization

The spatial arrangement of sp² hybrid orbitals is trigonal planar. Therefore, the angle between these orbitals is 120^oC. The atoms that undergo this hybridization have 1 un-hybridized p orbital because only two of three p orbitals are involved in this hybridization.

What is sp³ Hybridization

sp³ Hybridization is the mixing of one s atomic orbital with three p atomic orbitals. Here, the atoms do not have un-hybridized p orbitals because all three p orbitals are involved in hybridization. The resulting orbitals are known as sp³ hybrid orbitals. As same as for sp² orbitals, we can calculate the s and p characteristics of these orbitals.

In sp³ hybridization, we consider that all s and p orbitals as just atomic orbitals (s+p+p+p). The ratio between s and p orbitals is 1:3. Therefore the fraction of s orbital is ¼, and the fraction of p orbitals is ¾.  

S characteristic percentage = total atomic orbitals  x  (1/4) x  100%
                                                  = 25 %
p characteristic percentage = total atomic orbitals  x  (3/4)  x  100%
                                                  = 75 %

Figure 3: sp³ Hybridization

These orbitals are formed when one s orbital, and 3 p orbitals are hybridized. The resulting hybrid orbitals have about 25% of s characters and about 75% of p characters. The spatial arrangement of these orbitals is tetrahedral. Therefore, the angle between these orbitals is 109.5^oC.

Difference Between sp sp² and sp³ Hybridization

Definition

sp Hybridization: sp hybridization is the hybridization that takes place between an s atomic orbital and a p atomic orbital.

sp² Hybridization: sp² hybridization is the mixing of one s atomic orbital with two p atomic orbitals.

sp³ Hybridization: sp³ hybridization is the mixing of one s atomic orbital with three p atomic orbitals.

S Characteristics

sp Hybridization: The s characteristic percentage of sp hybrid orbitals is 50%.

sp² Hybridization: The s characteristic percentage of sp² hybrid orbitals is 33.33%.

sp³ Hybridization: The s characteristic percentage of sp³ hybrid orbitals is 25%.

P Characteristic Percentage of Hybrid Orbitals

sp Hybridization: The p characteristic percentage of sp hybrid orbitals is 50%.

sp² Hybridization: The p characteristic percentage of sp² hybrid orbitals is 66.66%.

sp³ Hybridization: The p characteristic percentage of sp³ hybrid orbitals is 75%.

Angle between Orbitals

sp Hybridization: The angle between sp orbitals is 180°C.

sp² Hybridization: The angle between sp² orbitals is 120°C.

sp³ Hybridization: The angle between sp³ orbitals is 109.5°C.

Geometry

sp Hybridization: The geometry of orbital arrangement in sp hybridization is linear.

sp² Hybridization: The geometry of orbital arrangement in sp² hybridization is trigonal planar.

sp³ Hybridization: The geometry of orbital arrangement in sp³ hybridization is tetrahedral.

Number of Un-hybridized Orbitals

sp Hybridization: Sp hybridization results in two un-hybridized p orbitals.

sp² Hybridization: Sp² hybridization results in one un-hybridized p orbitals.

sp³ Hybridization: Sp³ hybridization does not result in any un-hybridized p orbitals.

Conclusion

Hybridization in chemistry stands for the mixing of different atomic orbitals to form new hybrid orbitals with different characteristics. Sp, sp² and sp³ hybridizations are such examples. The main difference between sp, sp² and sp³ hybridization is that sp hybridization forms hybrid orbitals having 50% s orbital characteristics and sp² hybridization forms hybrid orbitals having 33% s orbital characteristics whereas sp³ hybridization forms hybrid orbitals having 25% s orbital characteristics.

Reference:

1.  “Hybrid Orbitals.” Chemistry LibreTexts, Libretexts, 21 July 2016, Available here.
2. “Orbital hybridisation.” Wikipedia, Wikimedia Foundation, 15 Jan. 2018, Available here.

Image Courtesy:

1. “Hybrydyzacja sp” By Joanna Kośmider – Own work (Public Domain) via Commons Wikimedia
2. “Hybrydyzacja sp2” By Joanna Kośmider – Own work (Public Domain) via Commons Wikimedia
3. “Hybrydyzacja sp3” By Joanna Kośmider – Own work (Public Domain) via Commons Wikimedia