Ethylene Lewis Structure Correct Answer And Explanation

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Ethylene, also known as ethene, is a simple hydrocarbon with the chemical formula Câ‚‚Hâ‚„. It is an important industrial chemical, widely used in the production of plastics, polymers, and other organic compounds. Understanding the Lewis structure of ethylene is crucial for comprehending its bonding characteristics and reactivity. In this comprehensive guide, we will delve into the intricacies of determining the correct Lewis structure for ethylene, exploring the fundamental principles and steps involved in the process.

Understanding Lewis Structures

Lewis structures, also known as electron dot diagrams, are visual representations of molecules that depict the bonding between atoms and the lone pairs of electrons present. These structures are based on the octet rule, which states that atoms tend to gain, lose, or share electrons in order to achieve a stable electron configuration with eight valence electrons (except for hydrogen, which aims for two electrons). Lewis structures provide valuable insights into the electronic structure of molecules, aiding in the prediction of molecular shapes, bond properties, and chemical reactivity.

Key Components of Lewis Structures

  • Chemical Symbols: Each atom in the molecule is represented by its chemical symbol (e.g., C for carbon, H for hydrogen).
  • Valence Electrons: Dots are used to represent valence electrons, which are the electrons in the outermost shell of an atom that participate in chemical bonding.
  • Covalent Bonds: Lines connecting atoms represent covalent bonds, which are formed by the sharing of electrons between atoms. A single line represents a single bond (two shared electrons), a double line represents a double bond (four shared electrons), and a triple line represents a triple bond (six shared electrons).
  • Lone Pairs: Pairs of dots not involved in bonding represent lone pairs, which are non-bonding electrons that belong to a single atom.

Determining the Lewis Structure for Ethylene (Câ‚‚Hâ‚„)

To determine the correct Lewis structure for ethylene (Câ‚‚Hâ‚„), we will follow a systematic approach involving several key steps:

1. Count the Total Number of Valence Electrons

First, we need to determine the total number of valence electrons in the molecule. Carbon (C) has four valence electrons, and hydrogen (H) has one valence electron. Ethylene (Câ‚‚Hâ‚„) has two carbon atoms and four hydrogen atoms. Therefore, the total number of valence electrons is:

(2 carbons × 4 valence electrons/carbon) + (4 hydrogens × 1 valence electron/hydrogen) = 8 + 4 = 12 valence electrons

2. Draw the Skeletal Structure

Next, we draw the skeletal structure of the molecule, connecting the atoms with single bonds. In ethylene, the two carbon atoms are bonded to each other, and each carbon atom is also bonded to two hydrogen atoms. This gives us the following skeletal structure:

H H
| |
C-C
| |
H H

3. Distribute the Remaining Electrons as Lone Pairs

Now, we distribute the remaining valence electrons as lone pairs around the atoms, starting with the most electronegative atoms (excluding hydrogen). In ethylene, carbon is more electronegative than hydrogen. We have already used 8 electrons to form the single bonds in the skeletal structure (4 single bonds × 2 electrons/bond = 8 electrons). This leaves us with 12 - 8 = 4 electrons to distribute.

We distribute these 4 electrons as lone pairs around the carbon atoms. However, each carbon atom already has 4 electrons around it (2 from the single bonds to hydrogen and 2 from the single bond to the other carbon). Adding lone pairs would exceed the octet rule for carbon, which states that carbon should have a maximum of 8 electrons around it.

4. Form Multiple Bonds to Satisfy the Octet Rule

Since we cannot add lone pairs to carbon atoms without exceeding the octet rule, we need to form multiple bonds. To satisfy the octet rule for both carbon atoms, we form a double bond between the two carbon atoms. This involves sharing two additional pairs of electrons between the carbon atoms.

The resulting Lewis structure for ethylene is:

H H
| |
C=C
| |
H H

In this structure, each carbon atom has 8 electrons around it (4 from the double bond and 2 from each single bond to hydrogen), and each hydrogen atom has 2 electrons around it (from the single bond to carbon). This structure satisfies the octet rule for all atoms in the molecule.

5. Verify the Formal Charges (Optional)

To further validate the Lewis structure, we can calculate the formal charges of each atom. The formal charge is the charge an atom would have if all bonding electrons were shared equally between the bonded atoms. The formula for calculating formal charge is:

Formal charge = (Valence electrons) - (Non-bonding electrons) - (1/2 × Bonding electrons)

For carbon in ethylene:

Formal charge = 4 - 0 - (1/2 × 8) = 0

For hydrogen in ethylene:

Formal charge = 1 - 0 - (1/2 × 2) = 0

Since all atoms in ethylene have a formal charge of 0, this Lewis structure is considered to be the most stable and correct representation of the molecule.

Analyzing the Correct Lewis Structure for Ethylene

The correct Lewis structure for ethylene reveals several important aspects of its bonding and molecular properties:

  • Double Bond: The presence of a double bond between the carbon atoms indicates that ethylene is an unsaturated hydrocarbon. A double bond consists of one sigma (σ) bond and one pi (Ï€) bond. The sigma bond is a strong, direct bond, while the pi bond is a weaker, sideways bond. The double bond makes ethylene more reactive than saturated hydrocarbons (alkanes) that contain only single bonds.
  • Planar Geometry: The double bond restricts rotation around the carbon-carbon bond, forcing the molecule to adopt a planar geometry. This means that all six atoms in ethylene lie in the same plane. The bond angles around each carbon atom are approximately 120 degrees.
  • Reactivity: The double bond in ethylene is a region of high electron density, making it susceptible to attack by electrophiles (electron-seeking species). This is why ethylene readily undergoes addition reactions, where other atoms or groups of atoms add across the double bond.

Incorrect Lewis Structures for Ethylene

It's essential to understand why certain Lewis structures for ethylene are incorrect. Some common mistakes include:

  • Violating the Octet Rule: Structures that show carbon atoms with more than eight electrons or hydrogen atoms with more than two electrons are incorrect.
  • Incorrect Number of Bonds: Structures that do not show a double bond between the carbon atoms or have an incorrect number of bonds to hydrogen atoms are incorrect.
  • Non-Zero Formal Charges: While formal charges are not always zero, structures with large formal charges on atoms are generally less stable and less likely to be correct.

Conclusion

Determining the correct Lewis structure for ethylene (Câ‚‚Hâ‚„) involves following a systematic approach, including counting valence electrons, drawing the skeletal structure, distributing remaining electrons as lone pairs, and forming multiple bonds to satisfy the octet rule. The correct Lewis structure reveals the presence of a double bond between the carbon atoms, which accounts for ethylene's planar geometry and high reactivity.

Understanding Lewis structures is fundamental to comprehending the bonding, properties, and reactivity of molecules. By mastering this skill, you can gain valuable insights into the world of chemistry and the behavior of chemical compounds.

This comprehensive guide has provided you with the necessary knowledge and steps to confidently determine the correct Lewis structure for ethylene and other molecules. By practicing these concepts, you will strengthen your understanding of chemical bonding and molecular structure.

Which of the following Lewis structures correctly represents ethylene (Câ‚‚Hâ‚„)? Options A, B, C, and D are given as diagrams. Please select the correct option.

Ethylene Lewis Structure Correct Answer and Explanation