What is the molecular geometry of CCl4?
A) tetrahedral
B) trigonal planar
C) linear
D) bent
E) trigonal pyramid
The correct answer and explanation is :
The correct answer is:
A) Tetrahedral
Explanation:
1. Lewis Structure of CCl₄
Carbon tetrachloride (CCl₄) consists of one carbon (C) atom and four chlorine (Cl) atoms. Carbon has 4 valence electrons, while each chlorine has 7 valence electrons. The total number of valence electrons in CCl₄ is:
- Carbon: 4
- Chlorine: (7 × 4) = 28
- Total: 32 valence electrons
The carbon atom forms four single covalent bonds with the chlorine atoms, using up 8 electrons (2 electrons per bond). The remaining 24 electrons are placed as lone pairs on the chlorine atoms.
2. VSEPR Theory Prediction
The Valence Shell Electron Pair Repulsion (VSEPR) theory states that electron pairs around a central atom arrange themselves to minimize repulsion. In CCl₄, carbon has four bonding pairs (no lone pairs on carbon). According to VSEPR theory, the AX₄ molecular shape corresponds to a tetrahedral geometry.
3. Bond Angles & Symmetry
- Bond angles: In a tetrahedral shape, the bond angles are approximately 109.5°.
- Symmetry: Since all four Cl atoms are identical, the molecule is perfectly symmetrical. This symmetry makes CCl₄ nonpolar, even though the C-Cl bonds are individually polar.
4. Why Not the Other Choices?
- B) Trigonal planar – Requires a central atom with three bonded atoms and no lone pairs (e.g., BF₃). CCl₄ has four bonded atoms, so it’s not planar.
- C) Linear – Requires only two bonded atoms and no lone pairs (e.g., CO₂).
- D) Bent – Occurs when a molecule has lone pairs on the central atom, like H₂O. Carbon in CCl₄ has no lone pairs.
- E) Trigonal pyramid – Requires a lone pair on the central atom (e.g., NH₃), which carbon in CCl₄ does not have.
Thus, CCl₄ has a tetrahedral molecular geometry.