When must parentheses be used in chemical formulas?

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When must parentheses be used in chemical formulas?

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Answer 1 · 2017-10-05T01:18:19

When you want to express a substance that has polyatomic ion or functional group (in organic chemistry).

Explanation:

There are two cases: polyatomic ions and polyatomic functional group.

[1] For example, Ammonium Chrolide $N H_{4} C l$ $NH_4Cl$ needs no parentheses because there is single $N H_{4}$ $NH_4$ ion in the formula.
Ammonium Sulfate should be expressed as ${(N H_{4})}_{2} S O_{4}$ $(NH_4)_2SO_4$ , as two ammonium ions and one sulfate ion are needed to balance the electron.

It must not be $N_{2} H_{8} S O_{4}$ $N_2H_8SO_4$ . People would wonder what $N_{2} H_{8}^{2 +}$ $N_2H_8^(2+)$ ion is...

[2] Another example can be seen in organic chemistry.
Xylene molecule has two methyl group on the benzene ring. It is expressed as $C_{6} H_{4} {(C H_{3})}_{2}$ $C_6H_4(CH_3)_2$
Ethylbenzene molecule has one ethyl group on the benzene ring and its condensed formula is $C_{6} H_{5} C_{2} H_{5}$ $C_6H_5C_2H_5$ .
Both xylene and ethylbenzene have $C_{8} H_{10}$ $C_8H_10$ formula but their structures are different.

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When must parentheses be used in chemical formulas?

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