They are organic in nature and as the name suggests, they are formed of only carbon and hydrogen. Sometimes, it also creates compounds with other varieties like sulfur, nitrogen, and so on. Although these are some of the simplest organic compounds we can come across, they have a varied range and differ in several physical and chemical properties.
Ethylene/Ethene
In this article, we will talk about one of the most common and widely used hydrocarbons: Ethylene(C2H4). Do you know that this compound is even lighter than air? Well, C2H4 is a simple straight-chain hydrocarbon that bears a sweet aroma and has a colorless form. Whenever we have read about organic chemistry, we have come across this compound, haven’t we? So, it is important for us to learn about C2H4 in detail to understand the nature of straight-chain hydrocarbons in a better manner.
Chemical Bonding in Hydrocarbons
Carbon has a covalent nature when it comes to bonding with hydrogen and this leads to the formation of the different types of hydrocarbons that we see. From simplest ones like methane and benzene to some of the complex ones like natural rubber, we deal with several HCs in our daily lives. In organic chemistry, we find hydrocarbons of several types: straight-chain, cyclic, and even branched. Straight-chains are the primary and most easily deciphered group of hydrocarbons. Here, we have:
Saturated hydrocarbons: Saturated hydrocarbons also called acyclic straight-chain alkanes follow the structure H-(CH2)n. They happen to form single bonds. Examples are methane and ethane. Unsaturated hydrocarbons: These form double and triple bonds and are known as alkenes and alkynes accordingly. Examples are acetylene and ethylene.
Chemical Bonding in Ethylene
Have you ever wondered how unique and vastly diverse the universe is? How this whole universe is built up by several atoms? Now, the atoms do not usually exist on their own in an isolated state, all we see around us are basically made up of atoms that have combined with each other to form molecules. Depending on the nature of atoms and their tendency to attract or repel another atom of a similar or different kind, we get resultant molecular compounds. And this whole process of two or more atoms coming close and deciding to stay together is known as chemical bonding. Now coming to ethylene, if we want to learn about it in a comprehensive manner, all we need to do to start is to understand its nature of bonding. For a carbon-hydrogen bond, this is covalent in nature. Going ahead, let us discuss this step by step.
C2H4 Lewis Structure
The electron dot structure, widely known as Lewis Structure, is a skeletal diagrammatic representation of a molecule taking into account the constituent atoms and the valence shell electrons. Before we jump right into this, we would like to introduce you to( or let’s say brush you up with in case you are already familiar) some really important concepts that will make your understanding of ethylene bonding way easier!
Valence electrons
An atom has a nucleus that is surrounded by negatively charged electrons which are present in different levels or shells. The outermost shell is known as the valence shell and the electrons present in that shell are known as valence electrons. The number of valence electrons of an atom is equivalent to its valency which in turn determines the combining capacity of the given atom.
Octet Rule
Have a look at the periodic table. If we see the last group, we can find out that all the elements are inert gases having eight electrons in their valence shells (except He which has two). The atoms of the main groups tend to gain more electrons to attain the same valency of eight. This is known as the octet rule or octet fulfillment.
C2H4 Lewis Structure Steps
The Lewis Structure of any molecule can be easily done if we follow certain given procedures. C2H4 is an unsaturated alkene. Let’s see how we can proceed with this: Step 1: How many atoms do we have in an ethylene molecule? 2 Carbon and 4 Hydrogen. Hydrogen is the first element in the periodic table, therefore it has only one valence electron. In the case of carbon, we have four valence electrons each. ∴ the total number of valence electrons in one molecule of C2H4 = 24+14 =12. Step 2: Now, that we have found out the total valence number, we get to check which atom is less electronegative. For hydrocarbons, we are always going to place the carbons in the center. Hydrogen atoms are going to take the outer positions. Step 3: Now, that we have drawn the atoms by their symbols, let us denote the valence electrons by dots.
Here, we can see that one carbon atom has its octet fulfilled(the Octet rule has been discussed before). But, the other central carbon atom lacks two electrons. So, what we can do is, we can take those electrons from the bottom and place them in the center between the two C atoms.
Step 4: We are done with the octet fulfillment concept. Since there are two bonds forming here, we will have a double bond structure. Hence, C2H4 is an alkene.
Here, we have got the most suitable and appropriate Lewis Structure Sketch of ethylene.
Molecular Geometry
When we draw the Lewis Structure of C2H4, we find a linear 2-D representation. In reality, the molecular shape of ethene is not linear. So, to understand chemical bonding, only sketching a lewis structure diagram is not sufficient. We need to focus on molecular geometry as well. Molecular geometry gives a clearer picture of the internal atomic chemistry by providing a three-dimensional viewpoint to the molecule. Not only that, we get to know other significant details like the bond angle and the length. C2H4, as we already know, is an alkene i.e. a hydrocarbon having a double bond. Take a look at the VSEPR theory which we will make use of to decipher the molecular geometry.
VSEPR
VSEPR stands for Valence Shell Electron Pair Repulsion model or theory. Like charges repel each other. So, the valence electrons being negatively charged have a tendency to repel each other within a molecule. VSEPR theory explains the shape by minimizing the electronic repulsion. Here, we need to deal with lone or unshared and bonded pairs of electrons.
For C2H4
In C2H4, if we look into the lewis structure, we will see that there are three bonded pairs of electrons around each carbon and zero lone pair. According to the VSEPR chart, the shape of the ethene molecule is trigonal planar. There are two triangles overlapping each other as we can see in the diagram. This is due to the fact that each carbon surrounds a planar triangle. The bond angle is around 120 degrees.
C2H4 Hybridization
Atomic orbitals combine together to form hybrid orbitals and the process is known as hybridization. The first and foremost thing that we need to look into while finding out the hybridization of any molecule is the electronic configuration of the atoms. C: 1s2 2s2 2p2 H: 1s1 In a double bond, we have one sigma and one pi bond. In a single bond, we have a sigma bond. So, here in C2H4, two sp2 hybrid orbitals, each from a carbon atom together combine to form a sigma bond. Also, the 2p orbitals (unhybridized, either 2py or 2pz) of the two carbon atoms combine to form the pi bond. This gives us the double(=) bond of C=C. The other sp2 hybrid orbitals form sigma bonds between C and H, therefore, leading to C-H single bonding structure.
C2H4 Molecular Orbital (MO) Diagram
The molecular orbital theory is a concept of quantum mechanics where atomic linearly combines to form molecular orbitals and we describe the wave nature of atomic particles. Here, bond strength depends on the overlapping degree which in turn depends on the spatial proximity of the combining atoms. Sigma orbital overlap: This signifies end interactions. Pi orbital overlap: This denotes side by side approach. Types of orbitals: We deal with three major types of orbitals- bonding, nonbonding, and antibonding orbitals. If we consider only the pi bonds, we can see that the unhybridized 2p orbitals( as discussed earlier in hybridization) now will form MO – a bonding and an antibonding orbital. The 𝝅 bonding orbital will see higher electron density which will hold the atoms together via nuclei attraction. The anti-bonding 𝝅*orbital will see a larger distance of electron density, therefore, weakening the bond and causing repulsion. The 𝝅CC stands for Highest Occupied Molecular Orbital or HOMO. The 𝝅CC *stands for LUMO( Lowest Unoccupied Molecular Orbital). ( the antibonding orbital remains empty).
The above diagram shows the Molecular Orbital(MO) diagram of ethene/ethylene.
Polarity of C2H4
The C2H4 molecule is non-polar in nature as all the atoms are symmetrically arranged across the molecule and both carbon atoms have the same influence on the bonded electrons. The molecule has uniform charge distribution across it and therefore the dipole moment of the molecule also turns out to be zero. For the more specific reasons regarding the polarity of C2H4, you must check out the article written on the polarity of C2H4. Below is the video regarding the drawing of lewis structure of C2H4. Have a look
Conclusion
Ethene or C2H4 is a common straight-chain acyclic alkene and an important member of organic hydrocarbons. Having a double C=C bond, it is unsaturated and this gives rise to several properties. Here, we learned about how to draw the proper Lewis Structure and find out the molecular geometry of an ethylene molecule. Furthermore, we discussed its hybridization and also mentioned the molecular orbital concept. In a nutshell, we have covered the bonding nature of ethylene. Thank you for reading!
