Question

The carbon-carbon bond length in ethylene is ________ than the carbon-carbon bond length in ethane, and the HCH bond angle in ethylene is ________ the HCH bond angle in ethane

Answer 1

Answer:

shorter

longer

Explanation:

The carbon-carbon bond length in ethylene is shorter than the carbon-carbon bond length in ethane, and the HCH bond angle in ethylene is longer the HCH bond angle in ethane.

The objective of this question is to let us understand the concept of Bond Length and Bond angle among the unsaturated aliphatic hydrocarbons (i.e alkanes, alkenes and alkynes).

The variation in bond angles of  unsaturated aliphatic hydrocarbons  can be explained by two concepts; The valence shell electron pair repulsion (VSEPR) model and hybridization.

The VSEPR model determines the total number of electron pairs surrounding the central atom of a species. The total number of electron pairs  consist of the bond pairs and lone pairs. All the electron pairs( lie charge ) will then orient themselves in such a way to minimize the electrostatic repulsion between them.

As the number of the lone pairs increases from zero to 2 ; the bond angles diminish progressively.

However;

Hybridization is the mixing or blending of two or more pure atomic orbitals (s,p and d) to form two or more hybrid atomic orbitals that are identical in shape and energy . e.g sp, sp² , sp³  hybrid orbitals etc .

The shape of the geometry of this compound hence determines their bond  angle.

The shape of the geometry of ethane is tetrahedral which is 109.5° in bond angle while that of ethylene is trigonal planar which is 120°.

This is why the HCH bond angle in ethylene is longer  the HCH bond angle in ethane .