Back Bonding

What is Back Bonding?

The exchange of electrons between an atomic orbital on one atom and an anti bonding orbital on another atom is known as back bonding.

Back bonding is a form of bonding that occurs between atoms in a compound when one atom has a single electron and the other has a vacant orbital next to it. Since pi-bonding occurs after the formation of the sigma bond, a compound with back bonding has pi-bonding characteristics.

Carbon monoxide can accept electrons back from the metal during back bonding of metal carbonyl, strengthening the bond between the metal and the carbon monoxide ligand. Back bonding is the mechanism of “accepting electrons back from the metal.”

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Back Bonding in BF3

Boron has an empty p-orbital, while fluorine has a lone pair of electrons in its p-orbital. As a result, boron is a Lewis acid, while fluorine is a Lewis base. Back bonding is a form of bonding in which fluorine donates a lone pair of electrons to boron atoms. 

Back Bonding in BF3

BF3 is a molecule made up of a Boron sp2 hybrid covalently bound to three fluorine atoms. The covalent bond indicates that electrons are exchanged rather than boron losing and fluorine gaining. Boron’s high ionization energy causes this bond to form. Three resonating structures result from the lone pair of electrons between boron and fluorine. Back bonding BF3 has no impact on the molecule’s bond angle, planarity, or geometry.

Back Bonding in BF3

The BF3 molecule has a ‘Trigonal Planar’ geometry. A model of three atoms around one atom in the centre is known as a ‘Trigonal Planar.’ It’s as if they’re all peripheral atoms in one plane, since the 120° bond angles on each of them make them an equilateral triangle.

Back Bonding in Metal Carbonyls

Any coordination or complex compound containing a heavy metal such as nickel, cobalt, or iron surrounded by carbonyl (CO) groups is known as a metal carbonyl. Tetracarbonylnickel Ni(CO)4, pentacarbonyliron Fe(CO)5, and octacarbonyl dicobalt Co2(CO)8 are some of the most common metal carbonyls.

Back Bonding in Metal Carbonyls

The bond between a metal and a Carbonyl group acting as a ligand. Pi-acid ligands, such as CO, are responsible for its formation. Pi-acid ligands have a single pair of electrons to donate to the metal atom and an empty anti bonding molecular orbital to back bond with the metal atom’s d-orbital electrons.

All about Back Bonding

  • Back bonding occurs as electrons pass from one atom’s atomic orbital to another atom’s or ligand’s anti-bonding orbital.
  • This form of bonding will occur between atoms in a compound when one atom has a lone pair of electrons and the other has a vacant orbital next to it.
  • As a result, the bonding takes on a partial double-bond character. Back bonding reduces the bond length while increasing the bond order.
  • Back-bonding is a form of resonance that can be visualized. Back bonding, in general, improves stability. It has an effect on molecule properties such as hybridization and dipole moment.

Pi Back bonding

Back bonding, also known as back donation, is a chemistry phenomenon in which electrons pass from one atom’s atomic orbital to an -acceptor ligand’s sufficient symmetry anti bonding orbital. The metal’s electrons are used to bind to the ligand, relieving the metal of excess negative charge in the process.

When one atom in a compound has a lone pair of electrons and the other has empty orbitals next to each other, this form of bonding occurs. Since pi-bonding occurs after the formation of a sigma bond, a compound with back bonding has pi-bonding characteristics. The bond angle is affected by back bonding. When a lone pair is required for back bonding on the central atom, the bond angle increases.

Pi Back bonding

Back bonding is a form of resonance that can be observed in a variety of chemical compounds. Back bonding is known to give chemical compounds more stability. It is also known to influence the molecule’s overall dipole moment and hybridization.

Frequently Asked Questions – FAQs

Is there back bonding in CCl2?

CCl2 is a well-known carbene in which carbon has a lone pair that can be donated to cl. Since cl has vacant d orbitals, c can easily form a pi dative bond (back bonding) with cl as 2p-3d backbonding.

Does back bonding affect bond length?

Back bonding BF3 has no impact on the molecule’s bond angle, planarity, or geometry. Notice that, as a result of back bonding, the hybridisation shifts, bond strength improves, and bond length decreases.

Why does BBr3 show least back bonding?

The size of orbitals increases when we switch from fluorine to chlorine, so there isn’t any efficient back bonding. Similarly, due to much larger changes in the size of overlapping orbitals, BBr3 would have less back bonding.

What is back bonding explained with example?

Bonding occurs between atoms in a compound when one atom has a lone pair of electrons and the other has a vacant orbital next to it. Since pi-bonding occurs after the formation of a sigma bond, a compound with back bonding has pi-bonding characteristics.

Why is Trisilylamine planar?

Because of its backbonding, trisilylamine has a planar geometry. The d-orbitals in silicon are empty. The empty d-orbital of silicon is supplied with electrons by the lone pair on the Nitrogen atom. Planar geometry is acquired by molecules with sp2 and sp hybridization.

What is synergic bonding?

The movement of electrons from ligands to metal is known as synergic bonding. The movement of electrons from ligand anti-bonding orbitals to filled metal orbitals. It’s a bond between a metal and a carbonyl group that acts as a ligand. Self-strengthening bonding is referred to as synergic bonding.

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