Ethene (C2H4) is also known as ethylene, it is the simplest member of the alkene class of hydrocarbons. It is an unsaturated organic compound with the chemical formula C2H4.
Ethene compound consists of two carbon atoms, bonded with each other through one pi and one sigma bond, and four hydrogen atoms, attached to carbon atoms through a sigma bond. It has a simple structure.
It does not contain any lone pair of electrons on carbon and hydrogen atoms.
Lewis Structure of Ethene (C2H4)
Table of Contents
Lewis structure is also called electron dot structure or dot and cross structure. The electron dot structure of ethylene or ethene contains four single bonds between carbon and hydrogen atoms and one double bond between two carbon atoms
Importance of Lewis Structure
Lewis structure is the pictorial representation of bond formation in a molecule. It helps us to know about the valance electrons and the arrangement of atoms in the molecule.
Steps to Draw the Lewis structure of Ethene
Steps to Draw a Lewis dot structure of ethene(C2H4) are given below;
Count Valance Electrons of Ethene
The Atomic Number of Hydrogen is= 1
Electronic Configuration of Hydrogen is=1s1
Number of Valence Electrons in Hydrogen is=1×4(as there are four hydrogens in the molecule) =4
The Atomic number of Carbon is= 6
Electronic Configuration of Carbon is=1s2 ,2s2 , 2p2
Number of Valence Electrons in Carbon is= 4×2(as there are two carbons in the molecule) =8
Now, find the total number of valence electrons by adding up the valence electrons of all six atoms:
Valence electrons of four hydrogen atoms + valence electrons of two carbon atoms
=4+8
Total valence electrons of Ethene= 12
Determine The Central Atom
As per the rule;
The Atom with the least electronegative value should be the central atom of the molecule. The electronegativity of carbon and hydrogen is 2.5 and 2.1 respectively. Although hydrogen is less electronegative than carbon, it cannot be the central atom. Because the central atom should bond with at least two other atoms.
Yet hydrogen has only one electron in its last shell, it cannot make more than one bond. So, carbon should be the central metal atom in the Lewis structure of ethylene. And hydrogen atoms should place in an outside position of the molecule.
Place the Valance Electrons Around the Atoms
Hydrogen has one electron; Carbon has four electrons around its atom like this:
If we observe the structure, we will notice that Hydrogen can share one electron with Carbon. Carbon and Hydrogen atoms share two electrons and they form single bonds with each other.
We have completed the valence shell for Hydrogens let us do the same for the Carbon atoms. Now each carbon atom has only two valence electrons. As it has shared two electrons with two Hydrogen atoms.
And so, Carbon will share its remaining two electrons with another carbon atom to complete its octet, resulting in the formation of a double bond between two carbon atoms.
Determine the Formal Charge on Ethene
We can calculate the formal charge on an atom by the following formula;
Formal charge = valance electrons -nonbonding electrons -bonding electrons/2
The formal charge on carbon atom:
Valence electrons=4
Bonding electrons=8
Nonbonding electrons=0
Formal charge = 4-0-8/2= 0
The formal charge on hydrogen atom:
Valence electrons=1
Bonding electrons=2
Nonbonding electrons=0
Formal charge = 1-0-2/2 = 0
Thus, all atoms (carbon and hydrogen) in the C2H4 Lewis structure contain zero formal charges.
Check the Stability by Calculating the Formal Charge on Ethene
As we have discussed that ethylene has zero formal charges. The specie with zero formal charges is non-reactive. It has stable bonding. Thus, the given Lewis structure is the most stable structure of C2H4.
Hybridization of Ethene
Lewis structure of ethene molecule consists of two carbons and four hydrogen atoms. Carbon has 6 electrons and hydrogen contains one electron.
Electronic configuration of carbon in its ground =1s2, 2s2, 2p2.
Electronic configuration of carbon in excited state= 1s2, 2s1, 2px1, 2py1 , 2pz1.
One of the electrons from the 2s orbital jump to the 2pz orbital in an excited state.
From the excited state only 2px, 2py, and 2s take part in hybridization and form three sp2 hybrid orbitals. One 2pz orbital remains unhybridized.
one sp2 orbital from each of the carbon forms c-c sigma bonds by head-to-head overlap, and the other two sp2 orbitals on each carbon overlap with a 1s orbital of hydrogen to form C-H sigma bonds.
Every carbon atom still has one half-filled 2pz orbital. These half-filled orbitals from each carbon form one pi bond between the carbons by side-by-side overlap, as a result, a double bond forms (one sigma bond and one pi bond)
Molecular Geometry and Shape of Ethene
The molecular geometry of a molecule helps us to understand its three-dimensional structure, arrangement of atoms in a molecule, and its shape. If we know the molecular geometry of a molecule. Then, it would be easy to study the reactivity, polarity, and biological activity of a molecule.
Ethylene has two different atoms i.e carbon and hydrogen. In ethene, each carbon joins with two hydrogen atoms in C2H4. Both these hydrogens repel each other according to VSEPR theory. Thus, ethene has trigonal planer geometry. Learn more about molecular geometry of BF3 here.
Determine the Geometry by AXN Notation
Valance shell electron pair repulsion theory is used to determine the molecular geometry of a molecule. This theory explains that the valance electrons pair surround the atom and arrange themselves in such a way that they face the least repulsion from each other.
VESPER theory explains geometry in the form of AXN notation.
The AXN notation is used to determine the molecular geometry of a molecule. In AXN notation ‘A’ denotes carbon atoms in a molecule
‘X’ denotes atoms connected to carbon, and
‘N’ denotes the number of lone pairs present on a molecule.
Formula Shape Bond Angle
AX2 Linear 180
AX3 Trigonal Planar 120
AX4 Tetrahedral 109.5
AX5 Trigonal Bipyramidal 120, 90
AX6 Octahedral 90
AX2N Bent 120
AX2N2 Bent 109.5
In ethylene ‘A’ stands for carbon, ‘X’ stands for two hydrogen atoms and one carbon atom bonded to carbon, and ‘N’ stands for zero because all electrons are involved in bonding. Ethylene contains the AX3 type of notation. Thus, has trigonal planer geometry.
The Bond Angle of Ethene
As the Lewis structure of the ethene molecule has trigonal planer geometry therefore the bond angle in ethene is 120o.
The Bond Length in Ethene
The distance between the nuclei of two bonded species is called “bond length”.
Bond length decreases with an increase in the number of bonds around the atom but in the case of ethylene carbon double bond carbon bond length is larger than carbon single bond hydrogen.
It is because carbon is more electronegative than hydrogen thus attracting shared electron pairs toward itself, shortening the bond length. While the double bond is between two similar atoms.
There is no attraction or repulsion for the shared electron pair. As a result, in the Lewis structure of C2H4, the bond length between two carbon atoms is 134 Pm and the bond length between carbon and hydrogen atoms is 108 Pm in ethene.
The Polarity of Ethene
Polarity is defined as the distribution of charge over the atom joined by a bond within a molecule. The charge appears on an atom due to electronegativity difference. When the electronegativity difference is more than 0.4, the bond will be polar.
However, in ethylene (C2H4) the electronegativity difference between the carbon and hydrogen bond is 0.4 which means that the bond is nonpolar. Thus, ethene is nonpolar.
The other reason for the non-polar nature of ethene is that each C-H bond in ethene is non-polar and has zero net dipole moment. Therefore, the whole molecule is nonpolar.
Molecular Orbital (MO) Diagram of Ethene
Molecular Orbital Diagram is a pictographic representation of bonding taking place between the electrons of the participating atoms to generate a new molecule.
The basic principle is that the atomic orbitals combine and overlap in such a manner to produce a similar number of molecular orbitals.
This occurs when electrons move from different orbitals to get distributed and redistributed within the participating orbitals.
In an excited state when electrons move from their original positions, bonding and antibonding orbitals are produced which produces the molecular orbital diagram specific for each molecule.
The ethylene molecule each carbon has one unhybridized p orbital which involves in the formation of the molecular orbital diagram of ethene. This unhybridized p orbital combine to form pi bonding and pi antibonding molecular orbitals. Pi bonding molecular orbital has a high electron density.
Sp2 hybridized orbitals of carbon atoms combine and overlap. As a result, form bonding sigma (σ) orbitals and antibonding sigma (σ*) orbitals. Learn more here about MOT of HCl
The Molar Mass of Ethene
Ethylene contains two carbon and four hydrogen atoms.
The molar mass of two carbon in ethylene=24.0214 g/mol
The molar mass of four hydrogens in ethylene=4.0318 g/mol
The molar mass of C2H4 =24.0214 g/mol+4.0318 g/mol= 28.0532g/mol
Uses of Ethene
- It uses for the artificially ripening of fruits.
- Ethylene uses for the production of anti-freezing agents (1,2-diol) used for motor car radiators.
- It involves the production of an anti-knocking agent for car engines.
- Ethylene uses for the Manufacturing of plastic, polythene, synthetic fiber terylene, and polypropene.
- It uses to prepare ethyl alcohol and acetaldehyde.
Properties of Ethene (C2H4)
The general properties of ethene are given below;
- Ethene is a colourless gas, which is lighter than air.
- It has a sweet odour.
- The melting point of ethene is169oC and the boiling point of ethene is 104oC.
- Ethylene is nonpolar. Thus, soluble in organic solvents such as benzene and carbon tetrachloride.
- It is less soluble in water.
Conclusion
- Ethene or C2H4 is a straight-chain unsaturated organic hydrocarbon having a C=C bond.
- There are twelve valence electrons and there are no unshared electrons for Ethene
- C2H4 is sp2 hybridized with a bond angle of 1200.
- It is a trigonal planer nonpolar molecule.
How many are sigma bonds and pi bonds formed in Ethene?
There are five sigma bonds. One sigma is between two carbon atoms by sp2-sp2 overlap. The other four sigma bonds formed between carbon and hydrogen atoms by sp2-S overlap. One pi bond formed between two unhybridized orbitals present on each carbon.
What is the IUPAC name and the common name of C2H4?
The IUPAC name of C2H4 is Ethene and the common name of C2H4 is ethylene.
What is the VSEPR geometry or shape of C2H4?
In ethene, there are three bonded pairs of electrons around each carbon and zero lone pairs.
According to the VSEPR theory, the geometry of the ethene molecule is trigonal planar.
What is the hybridization of Ethene(C2H4)?
Ethene shows sp2 Hybridization. In this process of Hybridization one, ‘s’, and two ‘p’ orbitals of each carbon mix. And form three new sp2 hybrid orbitals which all are the same in shape and have the same energy.