Draw an electron-dot structure for CH3-C=C-CO2- What the molecular geometry about the left carbon atom? (Shape) What the molecular geometry about the right carbon atom? (Shape) What the molecular geometry about each of the central two carbon atoms? (Shape)
The Correct Answer and Explanation is :
To answer your query, let’s first draw the electron-dot structure for the molecule CH3-C≡C-CO2^-. We will then discuss the molecular geometries around each carbon atom.
Electron-Dot Structure
The molecule can be sketched as CH3-C≡C-CO2^-. Here’s a breakdown:
- CH3: This group has a single carbon atom bonded to three hydrogen atoms.
- C≡C: A triple bond between two carbon atoms.
- CO2^-: A carbon atom double bonded to two oxygen atoms, carrying an extra electron to form a negative charge.
Molecular Geometry
- Left Carbon Atom (in CH3 group):
- This carbon is bonded to three hydrogen atoms.
- The geometry is tetrahedral due to the sp^3 hybridization, with bond angles close to 109.5 degrees.
- Right Carbon Atom (in CO2^- group):
- This carbon is double bonded to two oxygen atoms.
- The geometry is linear due to the sp hybridization, with a bond angle of 180 degrees.
- Central Two Carbon Atoms (in C≡C):
- Each of these carbon atoms is involved in a triple bond with each other and forms a single bond with another carbon.
- For the carbon attached to CH3, its geometry is linear as it is sp hybridized, directly involved in a triple bond and a single bond.
- The second carbon in the C≡C bond, attached to the CO2^-, also exhibits linear geometry, due to its sp hybridization.
Explanation
The geometry around each carbon atom is influenced by its hybridization and the types of bonds it forms:
- Tetrahedral Geometry: Occurs when a carbon atom is sp^3 hybridized, typically with four sigma bonds that spread out to minimize electron-pair repulsion, forming approximately 109.5-degree angles.
- Linear Geometry: Occurs with sp hybridization where the carbon atom forms two sigma bonds arranged at 180 degrees. This is typical in structures with double or triple bonds involving carbon.
These geometries follow the VSEPR (Valence Shell Electron Pair Repulsion) theory, which states that electron pairs around a central atom arrange themselves to minimize repulsion, thereby determining the molecule’s shape. For CH3, the electrons are spread in three dimensions forming a tetrahedral shape. In contrast, in C≡C and CO2^-, the electrons lie along a straight line, resulting in linear geometry.
Now, I will generate an image of the electron-dot structure for CH3-C≡C-CO2^- that visualizes these geometries.
Here is the electron-dot structure of CH3-C≡C-CO2^-, showing the molecular geometries around each carbon atom as discussed. You can see the tetrahedral geometry around the left carbon atom in the CH3 group, linear geometries around both central carbon atoms in the C≡C bond, and the linear geometry around the right carbon atom in the CO2^- group. This visualization includes the arrangement of electron pairs and indicates the negative charge on one of the oxygen atoms.