Question

Question #15598

Answer 1

There are two common methods for writing chemical formulas.

Explanation:

Method 1

Many chemists use the Hill system for writing chemical formulas,

There are two rules:

• If the molecule contains carbon, the elements are listed in the order `"C"`, then `"H"`, then all the other elements in alphabetical order.
• If there is no carbon, all the elements are listed alphabetically.

This gives us formulas like `"CH"_4` and `"H"_2"O"`.

This system is unambiguous and is used in most chemical databases and printed indexes to sort lists of compounds.

Method 2

Another common system puts the more positive elements in compound first.

This gives us formulas like `"H"_2"O"`, `"NaCl"`, and `"H"_2"SO"_4` (not `"ClH"` or `"H"_2"O"_4"S"`).

In practice, most chemists use Method 1 for organic compounds and Method 2 for inorganic compounds.

Nevertheless, it is permissible to depart from either method if you want to make a specific point.