Question

What is the correct name for $S{O_3}$?

Answer 1

Compounds which contain only two elements covalently bonded to each other are known as binary covalent compounds. Covalent inorganic compounds are named by using a procedure similar to that for ionic compounds and by using prefixes to indicate the number of atoms in the molecular formula.

Complete answer:
To name an inorganic covalent molecule, following steps must be followed:
1. The elements farthest to the left in the periodic table are generally named first. If both elements belong to the same group, then the element closer to the bottom is named first. In the case of $S{O_3}$, the sulphur is below oxygen and closer to the bottom of the column. Hence, sulphur will be named first in $S{O_3}$.
2. The second element is considered as a mono-atomic ion in an ionic compound even if it is covalently bonded, and named with a suffix $- ide$ along with the root of the name of the element. In the case of $S{O_3}$, the oxygen atom will be named as oxide.
3. If a molecule contains more than one atom of any element, then appropriate prefixes like di, tri, etc, are used along with the name of the element. In the case of $S{O_3}$, there are three oxygen atoms present in the molecule. Thus, it will be named as trioxide.
Hence, we can conclude that the correct name of $S{O_3}$ is Sulphur trioxide.

Note:
Ensure not to get confused between $S{O_3}$ which is a binary compound and $SO_3^{2 - }$ which is a polyatomic ion. Although the number of sulphur and oxygen atom in the molecule and ion are same but $S{O_3}$ is a neutral molecule whereas Sulphite ion i.e., $SO_3^{2 - }$ has two electrons extra and thus making it a negatively charged ion.