Valency of Carbon (Tetravalency) , Hybridization of Carbon, Tetravalence, Questions (For CBSE, ICSE, IAS, NET, NRA 2022)

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What is the Valency of Carbon?

  • The valency of carbon is four and one atom of carbon can make four covalent bonds.
  • The branch of organic chemistry deals with the compounds of carbon.
  • The valency of carbon is 4 and it is, therefore, said to be tetravalent
  • Due to the specific properties of the element, Carbon has established its importance among the other elements. The properties which make carbon so important are:
    • Catenation
    • Tetravalency
    • Size of a carbon atom

Hybridization of Carbon

  • Hybridization is the concept of combining atomic orbitals to make new hybrid orbitals appropriate to represent their properties of bonding. Hybridized orbitals are helpful in describing the shape of molecular orbitals apart from being a major part of valence bond theory.
  • Hybrid applies to the atomic orbitals that contribute to the hybridization. For example, in methane whose chemical formula is a set of orbitals develop by combining one s-orbital and three p-orbitals on the carbon atom. These orbitals direct towards the four hydrogen atoms placed at the vertices of a regular tetrahedron.
  • Ethene () consists of a double bond between the carbon atoms. Here, the carbon hybridizes by . In hybridization, the 2s orbital mingles with two among the three 2p orbitals available, making total orbitals with one remaining p-orbital. In ethane, two atoms of carbon develop a sigma bond by overlaying two orbitals, where every carbon atom makes two covalent bonds with hydrogen by overlapping all with angles. The pi bond among the carbon atoms develops by a overlap. The hydrogen-carbon bonds have equal length and strength that satisfies with experimental proof.
  • Many bonds also exist between non-similar atoms. When two atoms of oxygen are brought near opposite sides of the carbon atom in , one among the p orbitals on every oxygen makes a pi bond with anyone among the p-orbitals of carbon. Here, the sp hybridization forms two double bonds.

Hybridization

The carbon hybridizes in ethene since one π bond is needed for the double bond among the carbons and three σ bonds made for every carbon atom.

Hybridization of Carbon

Hybridization of Carbon

Tetravalence of Carbon

  • Ground state electronic configuration of carbon is . It has 4 valence electrons, so the probability of formation of four bonds is maximum. The bonds formed by the s orbital electrons will not be the same as that of p orbital electrons. So, in the formation of one molecule of , there will be a combination of 1 C atom with 4 H atoms.
  • The following types of bonds can be formed: and . Out of the four bonds, we have two ‘directional’ and two non-directional bonds . (Note: As we know that s orbitals are spherical in shape and do not have any specific direction and p orbitals have shapes in three directions x, y, and z-axis.) The strength of the bond will also differ as bond will be less strong than the bond as s overlapping is stronger.

Carbon at Ground State (Electronic Configuration)

  • Above electronic configuration of carbon shows that carbon has only 2 unpaired electrons. So, it can only form 2 bonds in its ground state.
  • Although we know carbon forms 4 covalent bonds. Here the concept of excited state comes. When carbon atoms get excited it shows following electronic configuration –

Carbon in Excited State (Electronic Configuration)

  • Now as can see above that carbon has 4 unpaired electrons in its excited state so it can form 4 covalent bonds with other atoms and this property of carbon is called tetravalency of carbon.
  • But practically all the bonds of are identical. This creates a problem. To solve this problem hybridization theory has been stated.
  • It is mainly a concept in which atomic orbitals are mixed with new hybrid orbitals which are most suited for the pairing of electrons to form chemical bonds. It can be understood by the fig given below:
An Electron Jumps from the 2 S Orbital To

An Electron jumps from the 2s orbital to the 2p orbital, resulting in four unpaired electrons

  • In the fig, three p and one s-orbital are hybridized to give four identical hybridized orbitals. In a similar manner, we can also get sp and hybridization. The only change will be that will have only two p orbitals. Now from the VSEPR theory, we know that sp and hybridized molecules are planar in structure. Whereas hybridized molecules take tetrahedral shape to become more stable (this structure leads to minimum energy state) .
  • The angle between each carbon and hydrogen atom is 109.5 in tetrahedral geometry, 120 in and 180 in sp hybridization. So, methane will have hybridization having a tetrahedral shape. Whereas examples for and hybridization are acetylene and ethene respectively that are planar in shape. Now we can clearly understand that ethane will have two unhybridized p orbitals from each carbon which will overlap with each other to form a pi bond.
  • So, by this, we can infer that a double bond is just a combination of two single bonds. The figure given below demonstrates the hybridization in the carbon atoms of ethylene and acetylene.
Hybridization of Carbon in Ethylene and Acetylene

Hybridization of Carbon in Ethylene and Acetylene

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