CCl4 Lewis structure: valence electrons and bonding picture
The formula CCl4 denotes carbon tetrachloride, a molecular compound with a central carbon atom bonded to four chlorine atoms. The ccl4 lewis structure is built from a complete valence-electron count and the octet rule for second-period carbon.
Valence-electron total
Carbon contributes \(4\) valence electrons and each chlorine contributes \(7\). The total for CCl4 is \[ 4 + 4 \times 7 = 32 \text{ valence electrons.} \]
Electron distribution and octet completion
Four single bonds connect carbon to four chlorines, accounting for \(4 \times 2 = 8\) electrons in bonding pairs. The remaining \(32 - 8 = 24\) electrons are placed as nonbonding electrons on chlorine atoms, giving \(24 / 4 = 6\) nonbonding electrons per chlorine, i.e., three lone pairs on each Cl. Carbon reaches an octet via four bonding pairs, and each chlorine reaches an octet via one bonding pair plus three lone pairs.
Formal charges and the preferred Lewis structure
A quick stability check uses formal charge: \[ \text{FC} = (\text{valence e}^-) - \left(\text{nonbonding e}^- + \frac{1}{2}\text{bonding e}^-\right). \] For carbon in CCl4, nonbonding electrons are \(0\) and bonding electrons are \(8\), so \(\text{FC}(C)=4-(0+4)=0\). For each chlorine, nonbonding electrons are \(6\) and bonding electrons are \(2\), so \(\text{FC}(Cl)=7-(6+1)=0\). The all-single-bond structure with three lone pairs on each Cl is therefore the zero-formal-charge Lewis structure.
Summary table for CCl4
| Quantity | Value for CCl4 | Meaning in the Lewis picture |
|---|---|---|
| Total valence electrons | \(32\) | All electrons placed as bonds or lone pairs |
| C–Cl bonds | 4 single bonds | \(8\) bonding electrons total |
| Lone pairs on each Cl | 3 lone pairs | \(6\) nonbonding electrons per chlorine |
| Formal charge | 0 on all atoms | Most stable electron-bookkeeping arrangement |
| Electron-domain geometry at C | Tetrahedral (AX4) | Four electron domains, no lone pairs on carbon |
| Approximate bond angle | \(\approx 109.5^\circ\) | Ideal tetrahedral angle |
Molecular shape and polarity
VSEPR predicts a tetrahedral molecular geometry because carbon has four bonding domains and no lone pairs. Although each C–Cl bond has a bond dipole, the tetrahedral symmetry causes dipole cancellation, so CCl4 is nonpolar as a molecule.
Common pitfalls
- Double bonds between C and Cl are not favored in the neutral molecule; the zero-formal-charge single-bond structure is preferred.
- Expanded octets are not used for second-period carbon; the octet on carbon in CCl4 is complete with four single bonds.
- Lone pairs belong on chlorine atoms, not on carbon; carbon has no lone pairs in the stable Lewis structure.