[xksen]

Hello. I am currently studying for my science exam and I am reviewing convalent compunds. I know it appears as a stupid question but, why don't elements like bromine, carbon, aluminum, etc. have prefixes in front of them? Thank you!

[wildfyr]

You answered it yourself: they are elements.

[sjb]

Having said that, sometimes you do put a prefix in front, to explicitly denote the number of atoms in the system.

For instance 2 mol of hydrogen atoms forms 1 mol of dihydrogen, or 3 mol of (di)oxygen is in equilibrium with 2 mol of ozone.

[wildfyr]

sjb is right, but we should keep in mind that for diatomic elements, the "di" is typically explicit from the context. If oxygen is present monatomically, that would be explicitly noted.

As with anything in chemsitry, we get exceptions, such as I₂ generally being known as plain iodine, but I₃^- is known as triiodide because it is an anion.

The best rule of thumb to offer is that elements do not get prefixes when present in their pure form at standard temperature and pressure (0°C 1 atm).