Benzene is an organic chemical compound with the molecular formula C6H6. Its molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each carbon atom. It is represented by a hexagon with a circle inside to denote the delocalized pi electrons, which are shared among all six carbon atoms, although traditionally, it was depicted with alternating single and double bonds (Kekulé structure).
The chemical benzene (C6H6) is nonpolar. It was first discovered by Michael Faraday in 1825 in the gas used for lighting in London, and its structure was later proposed by August Kekulé in 1865, famously inspired by a dream of a snake biting its own tail.
Benzene (C6H6) is a nonpolar molecule. Here’s why:
- Structure: Benzene has a planar, hexagonal ring structure where each carbon atom is bonded to one hydrogen atom and two other carbon atoms, forming a perfectly symmetrical ring.
- Bond Polarity: The C-H and C-C bonds in benzene are covalent. Carbon and hydrogen have similar electronegativities (C = 2.55, H = 2.20), making the C-H bonds only slightly polar. However, due to the symmetry of the molecule, these slight polarities cancel each other out.
- Symmetry: The arrangement of these bonds in benzene results in a molecule where all the electron pairs are evenly distributed around the ring. This symmetry ensures that there is no net dipole moment because the dipoles (if any slight ones due to C-H bonds) are vectorially balanced in all directions.
- Delocalization: The electrons in benzene are delocalized in a pi system above and below the plane of the ring. This delocalization further contributes to the uniformity of electron distribution, enhancing the nonpolar nature of the molecule.
Chemical Properties Influenced by Polarity (or lack thereof)
- Solubility:
- Benzene is soluble in nonpolar solvents like carbon tetrachloride (CCl4) or hexane, which is consistent with the “like dissolves like” principle. However, it is not very soluble in water (a polar solvent), because it cannot form hydrogen bonds with water molecules.
- Reactivity:
- Benzene’s electron-rich pi system makes it subject to electrophilic aromatic substitution reactions rather than addition reactions typical of alkenes. Its nonpolar nature influences how it interacts with reactants; often, the reactants need to be somewhat polarized or carry a charge to interact effectively with benzene’s pi electron cloud.
- Boiling and Melting Points:
- Benzene has a relatively low boiling point (80.1°C) and melting point (5.5°C) for a molecule of its size, which can be attributed in part to the weak van der Waals forces between nonpolar molecules. These intermolecular forces are weaker than the dipole-dipole interactions or hydrogen bonding found in polar compounds.
- Biological Impact:
- The nonpolar nature of benzene affects its behavior in biological systems. It can dissolve in lipid (fat) layers of cell membranes, which contributes to its toxicity since it can accumulate in fatty tissues.
- Use in Industry:
- Its nonpolarity makes benzene a good solvent for other nonpolar substances and it’s used in the synthesis of chemicals where a non-reactive, nonpolar solvent is needed. However, due to its toxicity and carcinogenic properties, alternatives are often sought.