Notes on Orbital Concept of Bonding | Grade 11 > Chemistry > Fundamental Principles of Organic Chemistry | KULLABS.COM

Orbital Concept of Bonding

  • Note
  • Things to remember

Covalent bond

A covalent bond between two atoms results from the overlap of an orbital of one atom with the orbital of another atom. When two orbital overlaps, they have the same region in space and a new orbital, called a molecular orbital (MO), is formed. Like an atomic orbital, a molecular orbital can accommodate only two electrons. A covalent bond is formed only if -

  • the two combining orbital are half-filled.
  • the bonding orbital approach each other in proper alignment needed for an effective overlap.
  • the electrons in the bonding orbitals have opposite spins.

Types of covalent bonds

There are two types of covalent bonds (molecular bonds) -

  1. Sigma (σ) bonds
  2. Pi (π) bonds

1) Sigma (σ) bond -This bond is formed by the linear or end to end overlap of two orbitals.

  • by the overlap of two 's' orbitals -a
  • by the overlap of px and s orbital-a
  • by the overlap of two endwise or head-wise or tail-wise overlap of px orbitals-a

Sigma bonds are symmetrical around the line drawn between the two nuclei. The electrons that occupy a sigma bond are called sigma (σ) electrons.

2)Pi (π) bond-A pi bond is formed by parallel or side to side overlap of two p-orbitals.

l

Like the p-orbitals from which it is obtained, a pi bond has two lobes. One-half of the pi bond lies above the plane containing the two nuclei and the other half lies below. The electrons that occupy a pi bond are known as pi (π) electrons.

There are two important differences between sigma and pi bonds-

(i) Pi electrons are loosely held than a pair of electrons in a sigma bond. They are of higher energy. As a result, pi-bonds are more easily broken and are more reactive than sigma bonds.

(ii) Rotation of atoms is not possible around a pi-bond. Sigma bonds are fixed and gives substitution reaction but pi-bonds are unstable, delocalised, and gives addition reaction.

Classes of carbon

There are four classes of carbon atoms-

  1. Primary carbon (1°) -If central carbon atom is attached with one carbon atoms or no other carbon atom, such type of carbon is known as 1° carbon.
  2. Secondary carbon (2°) - If central carbon atom is attached to two carbon atoms in a chain (alkane), such type of carbon is known as 2° carbon.
  3. Tertiary carbon (3°) -If central carbon atom is attached to three carbon atoms is a chain, such type of carbon is known as 3° carbon.
  4. Quaternary carbon (4°) -If central carbon atom is attached to four carbon atoms, such type of carbon is known as 4° carbon.

For example-

a

Reference

Adhikari, Rameshwar; Khanal, Santosh; Subba , Bimala; Adhikari, Santosh; Khatiwada, Shankar Pd. Universal Chemistry XI. First. Vol. 1st. Kathmandu: Oasis Publication, 2069.

Chaudhary, Ganga Ram; Karna, Shila Kant Lal; Sharma, Kanchan; Singh, Sanjay; Gupta, Dipak Kumar. A Textbook of Higher Secondary Chemistry XI. Ed. 2nd. Kathmandu: Vidyarthi Pustak Bhandar, 2069 (2012).





  • A covalent bond between two atoms results from the overlap of an orbital of one atom with the orbital of another atom.
  • There are two types of covalent bonds (molecular bonds) -Sigma (σ) bonds  and Pi (π) bonds

  • Sigma (σ) bond  is formed by the linear or end to end overlap of two orbitals. The two orbitals may be  s and s, p and s, and p and p.
  • Sigma bonds are symmetrical around the line drawn between the two nuclei. The electrons that occupy a sigma bond are called sigma (σ) electrons.

  • A pi bond is formed by parallel or side to side overlap of two p-orbitals.

  • Like the p-orbitals from which it is obtained, a pi bond has two lobes. One-half of the pi bond lies above the plane containing the two nuclei and the other half lies below. The electrons that occupy a pi bond are known as pi (π) electrons.
  • Pi electrons are loosely held than a pair of electrons in a sigma bond. They are of higher energy. As a result, pi-bonds are more easily broken and are more reactive than sigma bonds.
  • Rotation of atoms is not possible around a pi-bond. Sigma bonds are fixed and gives substitution reaction but pi-bonds are unstable, delocalised, and gives addition reaction.

  •  If central carbon atom is attached with one carbon atoms or no other carbon atom, such type of carbon is known as 1° carbon.

  • If central carbon atom is attached to two carbon atoms in a chain (alkane), such type of carbon is known as 2° carbon.
  • If central carbon atom is attached to three carbon atoms is a chain, such type of carbon is known as 3° carbon.
  • If central carbon atom is attached to four carbon atoms, such type of carbon is known as 4° carbon.
.

Very Short Questions

0%

ASK ANY QUESTION ON Orbital Concept of Bonding

No discussion on this note yet. Be first to comment on this note