CHEMICAL BONDING Identifying carbon hybridization in simple organic molecules Tag all the carbon atoms with pi bonds in this molecule. If there are none, please check the box below. H 1 H —C—C=C-H 1 H There are none.
The Correct Answer and Explanation is :
Let’s analyze the molecule you provided and identify the carbon atoms with pi bonds.
The molecule is:
H—C—C=C—H
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H HOr more simply:
H—C—C=C—H
(Each carbon with its hydrogens as shown)
Step 1: Understanding Pi Bonds
Pi (π) bonds occur when there is side-to-side overlap of p orbitals, usually found in double or triple bonds between atoms.
- A single bond is a sigma (σ) bond only.
- A double bond consists of one sigma and one pi bond.
- A triple bond consists of one sigma and two pi bonds.
So to find carbons with pi bonds, look for carbon atoms involved in double or triple bonds.
Step 2: Identify the carbons and their bonds
- The first carbon (leftmost) is bonded to hydrogens and one carbon by a single bond.
- The second carbon is bonded to the first carbon by a single bond and to the third carbon by a double bond (=).
- The third carbon is involved in a double bond with the second carbon.
Step 3: Identify carbons with pi bonds
- The second carbon is part of a double bond (C=C), so it has one pi bond.
- The third carbon is also part of that same double bond, so it has one pi bond.
The first carbon is only bonded by single bonds (sigma bonds) — no pi bonds.
Answer:
The second and third carbons have pi bonds.
Explanation (300+ words):
In organic chemistry, understanding the nature of bonds between carbon atoms is crucial to determining molecular geometry, reactivity, and properties. Carbon atoms form four bonds to complete their valence shell of eight electrons. These bonds can be single, double, or triple, with single bonds being sigma (σ) bonds, and double/triple bonds containing pi (π) bonds in addition to sigma bonds.
Pi bonds are formed by the sideways overlap of unhybridized p orbitals on adjacent atoms, which occurs only when there is a double or triple bond. This is different from sigma bonds, which result from head-on overlap of orbitals.
In the molecule H—C—C=C—H, there are three carbon atoms. The first carbon is bonded to two hydrogens and the second carbon, all with single bonds, which are sigma bonds. Therefore, it has no pi bonds. The second and third carbons are connected by a double bond (=), which means one of those bonds is a sigma bond, and the other is a pi bond.
Both carbons involved in this double bond share the pi bond equally because it exists between them. This pi bond restricts rotation around the bond axis and contributes to the rigidity and planarity of the molecule in that region. The presence of a pi bond is also a factor in chemical reactivity; double bonds are sites where many organic reactions occur.
Therefore, the carbons with pi bonds in this molecule are the second and third carbons — the ones connected by the double bond.
In summary:
- The first carbon is sp³ hybridized, bonded with single bonds only — no pi bonds.
- The second and third carbons are sp² hybridized, bonded by a double bond containing one pi bond.