Carbon disulfide (CS₂) is a covalent compound. Both carbon and sulfur are nonmetals, and they share electrons rather than transferring them. The electronegativity difference between carbon (2.55) and sulfur (2.58) is only 0.03 on the Pauling scale, which is far too small to create ionic bonds.
Why the Bonding Is Covalent
The quick rule for identifying bond type is straightforward: ionic bonds form between metals and nonmetals, while covalent bonds form between two nonmetals. Carbon and sulfur are both nonmetals, so CS₂ falls squarely in the covalent category.
Electronegativity confirms this. When two atoms have a large difference in electronegativity (typically above 1.7), one atom pulls electrons away from the other, creating ions and an ionic bond. Carbon and sulfur have almost identical electronegativities, 2.55 and 2.58, respectively. That difference of 0.03 means neither atom pulls electrons significantly harder than the other. Instead, the atoms share electrons in covalent bonds.
How the Atoms Are Arranged
Carbon disulfide has 16 valence electrons. The carbon atom sits in the center and forms a double bond with each of the two sulfur atoms. The structure looks like S=C=S, with the molecule arranged in a straight line. This linear shape is identical to what you see in carbon dioxide (CO₂), just with sulfur atoms in place of oxygen.
Because the molecule is perfectly symmetrical, the two bond polarities (already tiny, given how close the electronegativities are) point in exactly opposite directions and cancel each other out. The result is a dipole moment of exactly 0.0, meaning CS₂ is a nonpolar molecule overall.
How CS₂ Behaves Like a Covalent Compound
The physical properties of carbon disulfide line up perfectly with what you’d expect from a nonpolar covalent substance. It’s a volatile liquid at room temperature with a low boiling point, quite unlike ionic compounds, which tend to be solid at room temperature with very high melting points. It is nearly insoluble in water (about 2,160 mg/L at 25°C, which is very low), but it mixes freely with organic solvents like ethanol and ether. Ionic compounds show the opposite pattern: they dissolve well in water and poorly in organic solvents.
CS₂ also does not conduct electricity. Ionic compounds conduct when dissolved in water or melted because their ions are free to move and carry charge. Covalent compounds like CS₂ have no ions to begin with, so they can’t conduct current in any state.
The only intermolecular forces holding CS₂ molecules together are London dispersion forces, the weakest type. This is a direct consequence of the molecule being nonpolar. There are no dipole-dipole interactions and no hydrogen bonding. These weak forces explain why CS₂ evaporates quickly and is highly flammable, with vapors that can ignite from something as minor as the heat of a light bulb.
How CS₂ Compares to CO₂
Carbon disulfide and carbon dioxide are structural twins. Both have a central carbon atom double-bonded to two identical atoms in a linear arrangement. Both are nonpolar for the same reason: the symmetrical geometry cancels out any bond polarity. Both are covalent and both have a center of symmetry at the carbon atom.
The key difference is size. Sulfur atoms are larger than oxygen atoms, which gives CS₂ stronger London dispersion forces. That’s why CS₂ is a liquid at room temperature while CO₂ is a gas. The bonding concept, though, is the same in both molecules: purely covalent, with shared electrons holding the atoms together.