Chemistry by Inam Jazbi: Hybrid Molecular Structure of Methane, Ethane, Ethene and Ethyne

Hybrid Molecular Structure of Methane

In methane i.e. CH₄, carbon is bonded to four hydrogen atoms, thus carbon gets sp³-hybridized. Each H – C bond is sigma bond which is formed due to s-sp³ overlapping. There are four sigma bonds in CH₄. Thus CH₄ has tetrahedral geometry. Each bond angle in CH₄ is 109.28° (109.5°). The bond length between C–H is 1.09

Brief Description of Shape of Methane

Hybrid Molecular Structure of Ethene (Ethylene)

In ethene i.e. C₂H₄, each carbon is bonded to three other atoms (i.e. 2 H and 1 C atom) thus each carbon uses sp² hybrid orbitals plus unhybrid p_z orbital to make its bonds.

One sp²-hybrid orbital of each carbon atom overlaps linearly with other carbon to form a CH sigma bond. The remaining two sp²-hybrid orbitals of each carbon overlaps with 1s orbitals of hydrogen atoms to form four C-H sigma bonds. Now unhybridized p_z orbitals of each carbon overlap on parallel axis to form a pi bond between carbon to carbon.

There are five sigma bonds in C₂H₄, 4 in between C and H and one in between C and C, while one Pi bond in between C and C. Thus C₂H₄ has trigonal geometry. All bond angles (H-C-H and H-C-C) are 120°. Each C-H bond length is 1.09°A and each C=C bond length is 1.34°A (shorter than C-C bond length in CH₃-CH₃ which is 1.54°A).

Hybrid Molecular Structure of Ethyne (Acetylene)

In ethyne (acetylene), each carbon is bonded to two atoms (i.e. one H atom and one C atom) thus each carbon uses sp hybrid orbitals plus two unhybrid p_y and p_z orbitals to make its bonds.

One sp-hybrid orbital of each carbon atom overlaps linearly with sp orbital of other carbon to form a C-C sigma bond. The remaining sp-hybrid orbital of each carbon overlap with 1s orbital of Hydrogen atoms to form two C-H sigma bond. Two unhybrid atomic orbitals (2p_y and 2p_z) of each carbon overlap on parallel axis to form two pi bonds between C to C. All bond angles (H-C-C) is 180^○. Each C-H bond length is 1.09^○A and each C-C bond length is 1.2^○A (which is shorter than C-C and C=C bond lengths).