Draw the Lewis structure for HCCH (ethyne). – Draw the molecule by placing atoms on the grid and connecting them with bonds. – Include all hydrogen atoms and all lone pairs of electrons. Submit your answer.
The Correct Answer and Explanation is:
To draw the Lewis structure for ethyne (HCCH), also known as acetylene, we need to determine the arrangement of the atoms and bonds. Ethyne has the molecular formula C₂H₂. Here’s the step-by-step structure and explanation:
Step 1: Count the Total Valence Electrons
- Carbon (C) has 4 valence electrons, and there are 2 carbon atoms in the molecule: 4 x 2 = 8 electrons.
- Hydrogen (H) has 1 valence electron, and there are 2 hydrogen atoms: 1 x 2 = 2 electrons.
- Total valence electrons = 8 + 2 = 10 valence electrons.
Step 2: Arrange the Atoms
The structure of ethyne is linear with hydrogen atoms bonded to each carbon, and the carbons are bonded to each other. Arrange the atoms in this order: H–C≡C–H.
Step 3: Connect Atoms with Bonds
- Place a single bond between each hydrogen and carbon atom (H–C).
- Place a triple bond between the two carbon atoms (C≡C).
Step 4: Distribute Remaining Electrons
Each hydrogen is satisfied with 2 electrons (a single bond with carbon), and each carbon needs 8 electrons in total to satisfy the octet rule:
- Each C–H bond has 2 electrons (1 bond).
- Each C≡C triple bond has 6 electrons (3 bonds).
Step 5: Verify Octet Rule and Electron Count
Each carbon has 8 electrons (6 from the C≡C triple bond and 2 from the C–H bond). Hydrogens are satisfied with 2 electrons each.
Final Structure
The Lewis structure for HCCH (ethyne) is:
H–C≡C–HThis structure has:
- No lone pairs on any atom.
- Triple bond between the two carbons.
- Single bond between each carbon and hydrogen.
Explanation
In ethyne, each carbon forms three bonds with the other carbon (a triple bond) and a single bond with one hydrogen atom. This gives each carbon atom an sp hybridization, creating a linear shape with a bond angle of 180°. Triple bonds consist of one sigma (σ) bond and two pi (π) bonds. The pi bonds arise from the sideways overlap of p orbitals, while the sigma bond is a direct overlap along the internuclear axis.
The lack of lone pairs in the structure and the triple bond give ethyne unique properties, such as a high bond dissociation energy and a short C≡C bond length. Ethyne is also a relatively small molecule and is commonly used as a fuel in welding due to the high-energy bonds between carbon atoms.