GENERAL KNOWLEDGE

HYBRIDIZATION OF ATOMIC ORBITALS

Hybridization of atomic orbitals is a concept in chemistry that describes the mixing of two or more atomic orbitals to create new hybrid orbitals with different shapes, energies, and properties. This process occurs when an atom bonds with other atoms in order to form molecules.

The hybridization process is important because it helps to explain the geometries and properties of molecules. The most commonly encountered hybridization schemes are sp, sp2, and sp3 hybridization.

In sp hybridization, one s orbital and one p orbital combine to form two sp hybrid orbitals. These hybrid orbitals are linear in shape and oriented at a 180-degree angle to each other.

In sp2 hybridization, one s orbital and two p orbitals combine to form three sp2 hybrid orbitals. These hybrid orbitals are trigonal planar in shape and oriented at a 120-degree angle to each other.

In sp3 hybridization, one s orbital and three p orbitals combine to form four sp3 hybrid orbitals. These hybrid orbitals are tetrahedral in shape and oriented at a 109.5-degree angle to each other.

Other hybridization schemes are also possible, such as sp3d, sp3d2, and sp3d3 hybridization, which involve the mixing of s, p, and d orbitals. These hybridization schemes are important for understanding the shapes and properties of molecules that contain atoms with a high electron density, such as transition metals.

Overall, hybridization of atomic orbitals is an important concept in chemistry that helps to explain the shapes, energies, and properties of molecules.

 

Hybrid Orbitals Formation

Hybrid orbitals are formed by combining atomic orbitals in the same atom. This process is called hybridization, and it occurs when an atom needs to form covalent bonds with other atoms in a molecule. Hybridization involves mixing together two or more atomic orbitals with different energy levels and shapes to form a new set of hybrid orbitals with a different geometry.

The most common types of hybrid orbitals are sp, sp2, and sp3 orbitals, which are formed by hybridizing s and p orbitals. The number and type of hybrid orbitals formed depend on the number of electron pairs that an atom has available for bonding.

For example, in the case of carbon, which has four valence electrons in its outer shell, it can form four covalent bonds. In its ground state, carbon has two unpaired electrons in the 2s orbital and two unpaired electrons in the 2p orbitals. To maximize the number of covalent bonds that carbon can form, these orbitals hybridize to form four sp3 hybrid orbitals that are arranged in a tetrahedral geometry. The hybridization of carbon involves the mixing of one s orbital and three p orbitals, resulting in four hybrid orbitals that are equivalent in energy and shape.

Similarly, when nitrogen forms three covalent bonds, it undergoes sp2 hybridization, which involves the mixing of one s orbital and two p orbitals to form three hybrid orbitals in a trigonal planar geometry.

In summary, hybridization involves the mixing of atomic orbitals to form a new set of hybrid orbitals that are optimized for forming covalent bonds with other atoms in a molecule. The geometry and number of hybrid orbitals formed depend on the number and type of electron pairs available for bonding in the atom.

 

Description of sp, sp2, sp3 hybrid orbitals

Hybrid orbitals are classified according to the type of mixing of atomic orbitals involved. The three most common hybrid orbitals are sp, sp2, and sp3 hybrid orbitals.

  1. sp Hybrid Orbitals: sp hybrid orbitals are formed by the mixing of one s orbital and one p orbital of equal energy from the same atom. The resulting hybrid orbitals are two in number and are arranged linearly with an angle of 180 degrees between them. The sp hybrid orbitals are commonly found in atoms with two bonded atoms and no lone pairs of electrons. Examples of elements with sp hybrid orbitals include Be, B, C, and N.
  2. sp2 Hybrid Orbitals: sp2 hybrid orbitals are formed by the mixing of one s orbital and two p orbitals of equal energy from the same atom. The resulting hybrid orbitals are three in number and are arranged in a trigonal planar geometry with an angle of 120 degrees between them. The sp2 hybrid orbitals are commonly found in atoms with three bonded atoms and one lone pair of electrons. Examples of elements with sp2 hybrid orbitals include B, C, N, O, and F.
  3. sp3 Hybrid Orbitals: sp3 hybrid orbitals are formed by the mixing of one s orbital and three p orbitals of equal energy from the same atom. The resulting hybrid orbitals are four in number and are arranged in a tetrahedral geometry with an angle of 109.5 degrees between them. The sp3 hybrid orbitals are commonly found in atoms with four bonded atoms and no lone pairs of electrons. Examples of elements with sp3 hybrid orbitals include C, N, O, and F.

In summary, sp hybrid orbitals have two hybrid orbitals, sp2 hybrid orbitals have three hybrid orbitals, and sp3 hybrid orbitals have four hybrid orbitals. The number and arrangement of hybrid orbitals depend on the number of bonded atoms and the presence or absence of lone pairs of electrons.

 

Shapes of Hybrid Orbitals

The shapes of these hybrid orbitals are as follows:

  1. sp hybrid orbitals: The sp hybrid orbitals are formed by the mixing of one s orbital and one p orbital. The resulting hybrid orbitals have a linear shape. The angle between the two hybrid orbitals is 180 degrees.
  2. sp2 hybrid orbitals: The sp2 hybrid orbitals are formed by the mixing of one s orbital and two p orbitals. The resulting hybrid orbitals have a trigonal planar shape. The angle between the three hybrid orbitals is 120 degrees.
  3. sp3 hybrid orbitals: The sp3 hybrid orbitals are formed by the mixing of one s orbital and three p orbitals. The resulting hybrid orbitals have a tetrahedral shape. The angle between the four hybrid orbitals is 109.5 degrees.
  4. sp3d2 hybrid orbitals: The sp3d2 hybrid orbitals are formed by the mixing of one s orbital, three p orbitals, and two d orbitals. The resulting hybrid orbitals have a octahedral shape. The angle between the six hybrid orbitals is 90 degrees.

It’s important to note that the actual shapes of molecules depend on the arrangement of the hybrid orbitals around the central atom, which is determined by the number of bonding and nonbonding electron pairs in the molecule.

 

Molecular shapes in orbitals

  1. CH4 (methane) – It has a tetrahedral shape. The carbon atom is sp3 hybridized and forms four sigma bonds with four hydrogen atoms using its four hybrid orbitals.
  2. H2O (water) – It has a bent shape. The oxygen atom is sp3 hybridized and forms two sigma bonds with two hydrogen atoms using two of its hybrid orbitals. The remaining two hybrid orbitals form two lone pairs that repel the bonding pairs, giving the molecule a bent shape.
  3. NH3 (ammonia) – It has a trigonal pyramidal shape. The nitrogen atom is sp3 hybridized and forms three sigma bonds with three hydrogen atoms using three of its hybrid orbitals. The remaining hybrid orbital forms a lone pair that repels the bonding pairs, giving the molecule a trigonal pyramidal shape.
  4. BCl3 (boron trichloride) – It has a trigonal planar shape. The boron atom is sp2 hybridized and forms three sigma bonds with three chlorine atoms using three of its hybrid orbitals. The remaining hybrid orbital is unhybridized and contains no electrons, giving the molecule a trigonal planar shape.
  5. C2H2 (acetylene) – It has a linear shape. The carbon atoms are sp hybridized and form a triple bond between them using their two hybrid orbitals each. The remaining two hybrid orbitals of each carbon atom form sigma bonds with two hydrogen atoms each.
  6. BeCl2 (beryllium chloride) – It has a linear shape. The beryllium atom is sp hybridized and forms two sigma bonds with two chlorine atoms using its two hybrid orbitals. The remaining two hybrid orbitals are unhybridized and contain no electrons, giving the molecule a linear shape.
  7. C2H4 (ethylene) – It has a planar shape. The carbon atoms are sp2 hybridized and form a double bond between them using their two hybrid orbitals each. The remaining hybrid orbitals of each carbon atom form sigma bonds with two hydrogen atoms each.
  8. SF6 (sulfur hexafluoride) – It has an octahedral shape. The sulfur atom is sp3d2 hybridized and forms six sigma bonds with six fluorine atoms using its six hybrid orbitals.

 

Sigma and Pi Bonds

A sigma bond is formed when two atomic orbitals, which have the same energy and are pointing towards each other, overlap and share a pair of electrons. This overlap of orbitals is known as a “head-on” overlap. The resulting bond is a single bond and is characterized by the presence of a cylindrical electron density distribution along the internuclear axis. Sigma bonds can form between s-s, s-p, p-p, and even d-p orbitals.

A pi bond, on the other hand, is formed when two parallel atomic orbitals overlap and share a pair of electrons. This overlap of orbitals is known as a “sideways” overlap. Pi bonds typically form between two unhybridized p orbitals, which are perpendicular to the internuclear axis. The resulting bond is weaker than a sigma bond, and is characterized by a cloud of electron density above and below the internuclear axis.

In molecules, double and triple bonds are formed by the combination of one or two sigma bonds with one or two pi bonds. For example, a carbon-carbon double bond consists of one sigma bond and one pi bond, while a carbon-carbon triple bond consists of one sigma bond and two pi bonds.

Overall, sigma and pi bonds are essential in the formation of stable molecules and play a crucial role in determining the chemical and physical properties of compounds.

 

Description of sigma and pi bonds using C2H2 and C6H6

Sigma and pi bonds are two types of covalent bonds that can form between two atoms.

A sigma bond is formed when two atomic orbitals overlap end-to-end, with the electron density concentrated along the axis between the two nuclei. A single bond between two atoms always consists of one sigma bond.

On the other hand, a pi bond is formed when two atomic orbitals overlap side-by-side, with the electron density concentrated above and below the axis between the two nuclei. A pi bond is weaker than a sigma bond and is usually formed in addition to a sigma bond in double or triple bonds.

Let’s consider the molecules C2H2 and C6H6 to understand the difference between sigma and pi bonds.

C2H2 (ethyne or acetylene) has two carbon atoms bonded together by a triple bond. The triple bond consists of one sigma bond and two pi bonds. The sigma bond is formed by the overlap of the sp hybridized orbitals of the two carbon atoms, while the two pi bonds are formed by the overlap of the unhybridized p orbitals. The pi bonds are perpendicular to the sigma bond.

C6H6 (benzene) has a ring of six carbon atoms bonded together by alternating single and double bonds. The carbon-carbon double bonds consist of one sigma bond and one pi bond. The pi bond is formed by the overlap of the parallel p orbitals of the carbon atoms, while the sigma bond is formed by the overlap of the sp2 hybridized orbitals. The pi bonds in benzene are delocalized over the entire ring, which gives the molecule its characteristic stability and planar geometry.