Orbital Bonding in Ethene

Carbon bonds are covalent, comprising either sigma or bonds. Single, double, and triple bonds can be formed by carbon. The structure is determined by the number of bonds it forms. Carbon has a tetrahedral structure with four single bonds, a trigonal planar structure with one double bond, and a linear structure with a triple bond.

A single carbon atom possesses four electrons: two in the 2s orbital, one in each of the 2p_x and 2p_y orbitals, and no electrons in the 2p_z orbital. A single carbon atom has the ability to form up to four bonds, but due to its electron configuration, this is not possible because there are only two electrons available to connect with. The other two are in a lone pair state, which makes them far less reactive to a single electron. To form the four bonds, the carbon atom promotes one of its 2s electrons into the unoccupied 2p_z orbital, leaving it with four unpaired electrons and allowing it to form four bonds. The electron does not promote itself. When a photon of light of the correct wavelength strikes a carbon atom, it promotes it. When this photon strikes a carbon atom, it provides enough energy for one of the lone pair electrons to be promoted to the 2p_z orbital.

Orbital Bonding in Ethene

Valence bond theory has only been able to describe the bonding in molecules with single bonds so far. When molecules have double or triple bonds, however, the model requires more information. The simplest chemical with a carbon double bond is ethylene (often known as ethene), CH₂CH₂. Ethylene has one carbon-carbon double bond and four carbon-hydrogen single bonds, according to its Lewis structure. The four carbon-hydrogen bonds in the ethylene molecule have been proved to be similar in an experiment. The molecule should have a trigonal planar geometry, according to VSEPR theory, because each carbon is surrounded by three electron groups. Despite the fact that each carbon has met its tetravalent criterion, one bond appears to be different. Clearly, this is a different form of orbital overlap.

A different type of hybrid orbital participates in the formation of sigma bonds in ethene. The 2s, 2p_x, and 2p_y atomic orbitals on each carbon unite to produce three  sp²hybrids, leaving the 2p_zorbital unhybridized. Three of each carbon’s four valence electrons are dispersed among the three sp² hybrid orbitals, with the fourth electron remaining in the unhybridized p_z orbital. ” sp²-hybridized carbon” describes each carbon in ethene. There are four unpaired electrons to form bonds in the electron configuration of the sp² hybridised carbon. However, because the unpaired electrons are trapped in two different sorts of orbitals, two different types of bonds are expected to form.

Mathematically, the form of the sp²-hybridized orbital is essentially the same as that of the sp³-hybridized orbital. The three sp²-hybridized orbitals are placed in a trigonal planar layout to reduce electron repulsion. Each orbital lobe points to the three corners of an equilateral triangle, forming a 120-degree angle between them. Trigonal planar geometry and sp²Hybridization are attributes of atoms surrounded by three electron groups.

The plane of the trigonal planar sp² hybrid orbitals is perpendicular to the unhybridized 2p_y orbital.

Each carbon atom in the ethylene molecule is linked to two hydrogen atoms. For the C-H sigma bonds in ethylene (sp² (C)-1s), overlap two sp²-hybridized orbitals with the 1s orbitals of two hydrogen atoms (H). As a result, the four carbon-hydrogen bonds in ethylene are identical, as predicted by the data.

The overlap of a sp²a hybrid orbital from each carbon forms the C-C sigma bond in ethylene.

The ethylene molecule’s sigma bond framework is formed by the overlap of hybrid orbitals or a hybrid orbital and a 1s orbital from hydrogen. On each carbon, however, the unhybridized p_z orbital persists.

Carbon’s unhybridized  p_z orbitals overlap to form a bond (pi). p_z (C)-1pz is a typical notation for orbital overlap (C). In most chemical compounds, numerous bonds are created by the overlap of unhybridized p orbitals. It’s worth noting that ethene’s carbon-carbon double bond is made up of two separate sorts of bonds: sigma and pi.

Ethylene is stated to have five sigma bonds and one pi bond in total. Pi bonds are weaker than sigma bonds because the p orbitals overlap side-by-side, resulting in a less effective orbital overlap when compared to a sigma bond’s end-to-end orbital overlap.

Five sigma bonds and one pi bond are said to make up an ethylene molecule. The three sp² hybrid orbitals on each carbon provide the basic trigonal planer shape. In ethylene, the H-C-C bond angle is 121.3 degrees, which is extremely close to the 120 degrees predicted by VSEPR. In ethylene, there are four C-H sigma bonds. In comparison to the carbon-carbon single bond in ethylene (154 pm & 377 kJ/mol), the carbon-carbon double bond in ethylene is both shorter (133.9 pm) and nearly twice as strong (728 kJ/mol). Each of ethylene’s four carbon-hydrogen bonds is equivalent, with a length of 108.7 pm.

Electronic Configuration

The valence orbitals in ethene must be calculated and their relative stability compared.

When we consider carbon in its ground state, we can see that its electrical arrangement is 1s²2s²2s²

In the 2p subshell, there are four valence electrons, but only two of them are unpaired.

As carbon has only two unpaired electrons in its ground state, it can only form two bonds.

As a result, an electron in the 2s subshell will be promoted to the 2p subshell, causing carbon to undergo excitation.

We now have four unpaired electrons, allowing carbon to form four bonds.

The overall shape of carbon in ethene will not be trigonal planar if it forms bonds directly using 2s orbitals (spherical) and 2p orbitals (dumb-bell shaped).

Carbon Atom

The formal IUPAC nomenclature for H₂C=CH₂ is ethene, however it is also known as ethylene. The name Ethylene comes from the fact that it resembles the ethyl group (CH₂CH₃) but has a double bond between the two carbon atoms. Ethene has the simplest alkene formula (C₂H₄) because it has the fewest carbons (two) required for a carbon-carbon double bond.

Conclusion

Ethene is made up of two 2s²2p_x¹2p_y² carbon atoms and four 1s¹ hydrogen atoms. These carbon atoms already have four electrons, but they each desire four more to fill the valence shell to a total of eight. Carbon has the same electron configuration as neon, a noble gas, because it has eight valence electrons around it. Carbon aspires to have the same configuration as Neon because it is at its most stable, lowest energy state when it has eight valence electrons; it has all of the electrons it requires and is no longer reactive.