Which of the following is the correct Lewis structure for dicarbon tetrahydride, [tex]C_2H_4[/tex], also known as ethene?
Answer (2)
Calculate the total valence electrons for C2H4: 12 electrons.
Form a single bond between the two carbon atoms and add two hydrogen atoms to each carbon.
Calculate the number of electrons used: 10 electrons.
Form a double bond between the carbon atoms with the remaining 2 electrons, resulting in the correct Lewis structure:
H H
C=C
H H
Explanation
Understanding the Problem We want to determine the correct Lewis structure for ethene (C2H4). A Lewis structure shows how atoms are arranged and bonded in a molecule.
Calculating Valence Electrons First, let's calculate the total number of valence electrons in C2H4. Carbon (C) has 4 valence electrons, and hydrogen (H) has 1. So, for C2H4, we have:
( 2 carbon atoms × 4 valence electrons/carbon ) + ( 4 hydrogen atoms × 1 valence electron/hydrogen ) = 8 + 4 = 12 valence electrons
This means we have 12 electrons to distribute in our Lewis structure.
Arranging the Atoms Now, let's consider the arrangement of atoms. Ethene has two carbon atoms, so they must be bonded to each other. We can start by drawing a single bond between the two carbon atoms (C-C). Each carbon atom also needs to bond to two hydrogen atoms. So, we place two hydrogen atoms on each carbon atom.
Counting Electrons Used Let's count how many electrons we've used so far. We have 5 single bonds (1 between the carbons and 4 between carbon and hydrogen), and each bond represents 2 electrons. So, we've used:
5 single bonds × 2 electrons/bond = 10 electrons
We started with 12 valence electrons, and we've used 10, so we have 2 electrons remaining.
Forming the Double Bond The remaining 2 electrons must form another bond between the two carbon atoms. This creates a double bond (C=C). Now, let's check if each atom satisfies the octet rule (or duet rule for hydrogen). Each carbon atom has 4 bonds (2 single bonds to hydrogen and a double bond to the other carbon), which means each carbon has 8 electrons around it (an octet). Each hydrogen atom has 1 bond, which means it has 2 electrons around it (a duet).
Final Lewis Structure Therefore, the correct Lewis structure for ethene (C2H4) has a double bond between the two carbon atoms and two single bonds to hydrogen atoms on each carbon atom. This corresponds to the structure:
H H
C=C
H H
Examples
Understanding Lewis structures is crucial in various fields. For instance, in designing new materials, chemists use Lewis structures to predict how molecules will interact. In environmental science, they help in understanding the behavior of pollutants. Moreover, in pharmacology, Lewis structures aid in designing drugs that interact specifically with target molecules in the body. By visualizing the electron distribution, scientists can better predict molecular properties and design new compounds with desired characteristics.
The Lewis structure for ethene (C2H4) features a double bond between the two carbon atoms and single bonds to four hydrogen atoms. Each carbon atom is bonded to two hydrogen atoms, satisfying the octet rule for carbons and duet rule for hydrogens. The total valence electron count is 12, which is correctly used in forming these bonds.
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