Equation Notation [ENDORSED]

[torialmquist1F]

When writing chemical equations, why are some atoms paired together in parenthesis with a subscript?
For example Ca5(PO4)3OH
Does this mean that the 3 applies to all elements in the parenthesis?

[sandros]

Usually, when you use subscripts, you refer to the element that precedes it. For example: C6H12O6 implies that there are 6C, 12H and 6O in this compound). However, when you use parentheses, the subscript refers to all the elements inside the parentheses. For example, Si(HCO3)4 implies that there are 4H, 4C and 4x3=12 O in this compound.

Hope this helps.

[CalebBurns3L]

You are correct. If a subscript follows a group of elements isolated with parenthesis, then the subscript applies to every element in that group. To further clarify your question, the reason that some atoms are paired together in parenthesis is to denote the presence of a polyatomic ion and to show how many polyatomic ions are in the compound.