What is the structure of benzene?
Benzene is one of the most important organic molecules, and can be thought of as a bridge or first step from introductory chemistry subjects to organic chemistry or industrial synthesis. It is also called an "aromatic ring" because many of its compounds have strong and often characteristic scents associated with them.
Benzene's fundamental structure is a hexagonal ring. Rings, in organic chemistry, are self-contained sequences of bonds with no real beginning or end, except those arbitrarily chosen through naming conventions such as IUPAC in order to be able to talk about them universally. Benzene has 6 carbons, so these form the core of the ring.
Benzene also has three double bonds between these carbons. The bonds are spaced out, so that they alternate with single bonds between each of the carbons. Further, the ring experiences a phenomenon called resonance; there is no particular reason why the double bonds need to be on one particular carbon or another, so they average themselves out over all 6. This means each carbon experiences slightly more than the carbon-carbon bond strength that would be found in a single bond, but slightly less than what would be felt in a double bond. This is often represented symbolically as a circle inside the hexagonal ring.
Finally, the remaining bond spaces on the carbon are filled with hydrogens. Since each carbon is already experiencing three carbon-carbon bonds, this leaves only one space for a hydrogen to bond with each carbon. In terms of molecular geometry, the carbon-carbon bonds lock the ring into a planar arrangement, and so each carbon-hydrogen is planar with this as well, and the entire molecule can be thought of as a two-dimensional planar arrangement.