Be sure to answer all parts. Draw Lewis structures for CCl
and C
Cl
. Give the molecular shape around each carbon atom. Explain why the carbon atoms in the two molecules have different shapes. CCl
is tetrahedral since carbon has four groups around it. Each C in C
Cl
has trigonal planar geometry since each carbon has three groups around it.
The Correct Answer and Explanation is:
Lewis Structures
1. CCl₄ (Carbon Tetrachloride):
- Central atom: Carbon (C)
- Bonds: 4 single bonds with 4 chlorine (Cl) atoms
- Electron regions around carbon: 4 bonding pairs
Lewis structure:
markdownCopyEdit Cl
|
Cl – C – Cl
|
Cl
2. C₂Cl₄ (Tetrachloroethylene):
- Atoms: Two carbon atoms double bonded to each other (C=C)
- Each carbon also has two single bonds to chlorine atoms.
Lewis structure:
mathematicaCopyEditCl Cl
\ /
C = C
/ \
Cl Cl
Molecular Shapes
- CCl₄: The central carbon is surrounded by four electron groups (4 single bonds), which arrange themselves in a tetrahedral geometry (bond angles ≈ 109.5°).
- C₂Cl₄: Each carbon atom is bonded to:
- One carbon (via a double bond)
- Two chlorine atoms (via single bonds)
- Total: 3 regions of electron density → Trigonal planar geometry (bond angles ≈ 120°)
Explanation
The molecular shapes of CCl₄ and C₂Cl₄ differ due to differences in the number and types of electron groups surrounding each carbon atom. In carbon tetrachloride (CCl₄), the carbon atom forms four single covalent bonds with chlorine atoms. These four electron pairs repel each other equally and arrange themselves as far apart as possible in three-dimensional space, resulting in a tetrahedral shape with bond angles of approximately 109.5°. There are no lone pairs on the central carbon, only bonding pairs.
In contrast, tetrachloroethylene (C₂Cl₄) consists of two carbon atoms connected by a double bond. Each carbon is also bonded to two chlorine atoms, giving each carbon a total of three regions of electron density (one double bond and two single bonds). According to VSEPR (Valence Shell Electron Pair Repulsion) theory, three regions of electron density adopt a trigonal planar geometry, with bond angles close to 120°. The double bond between the carbon atoms introduces a planar arrangement, which keeps all atoms in a flat geometry.
The different geometries arise from the different types of bonding and electron arrangements: four single bonds around one carbon (CCl₄) leads to a 3D tetrahedral structure, while three groups (including a double bond) around each carbon in C₂Cl₄ leads to a flat trigonal planar shape. These differences impact the physical and chemical behavior of the molecules, such as polarity and reactivity.
