# What does a subscript following an element in a chemical formula mean?

Aug 15, 2017

It usually specifies the standard state of the element......

#### Explanation:

Sometimes the state is fairly obvious....

${H}_{2} \left(g\right) + \frac{1}{2} {O}_{2} \left(g\right) \rightarrow {H}_{2} O \left(l\right)$

..i.e dihydrogen and dioxygen are gases, whereas water is a liquid under standard conditions. And of course we could use the state symbols to represent phase changes.

${H}_{2} O \left(l\right) \rightarrow {H}_{2} O \left(s\right) + \Delta$

$N a C l \left(s\right) + \Delta \rightarrow N a C l \left(l\right)$

And in aqueous solution, so-called $\text{aquated}$ ions are represented....

$N a C l \left(s\right) \stackrel{{H}_{2} O}{\rightarrow} N {a}^{+} \left(a q\right) + C {l}^{-} \left(a q\right)$

Where $N {a}^{+} \left(a q\right)$ represents the aquated ion, probably ${\left[N a {\left(O {H}_{2}\right)}_{6}\right]}^{+}$ and $C {l}^{-} \left(a q\right) \equiv {\left[C l {\left({H}_{2} O\right)}_{4 - 6}\right]}^{-}$.