Why is $\ce{Ba(OH)2}$ Barium hydroxide not Barium dihydroxide?
Why is Lithium carbonate $\ce{Li2CO3}$ instead of $\ce{LiCO3}$?
Is there a formula or is just the case for these two?
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Sign up to join this communityWhy is $\ce{Ba(OH)2}$ Barium hydroxide not Barium dihydroxide?
Why is Lithium carbonate $\ce{Li2CO3}$ instead of $\ce{LiCO3}$?
Is there a formula or is just the case for these two?
There is no other Ba(OH)x so there is no need to note a difference between several forms.
This happens with any metal ion that only attains precisely one positive charge, whether it is +1 or +10.
Lithium ions have +1 charge. Carbonate ions have -2 charge. Therefore to balance the charge in the formula we need 2 lithium to 1 carbonate.
This happens with all formulae, and it is a simple mathematical check to decide what the correct ratios should be.
This is the general process to write the formula for an ionic name.
Ex. Barium [Charge not needed] Hydroxide
Manganese (IV) Oxide
Lithium [Charge not needed] Carbonate
Charges:
Formula
The reducing subscripts and straightforward nature (only one right way to do it) are due to how these ionic formulas are "formula units" written to be neutral, as in the actual form, the ions form crystal lattices which can be described as large collections of these ratios.
It all depends on the valency of the atoms involved.
If you are have 1st group elements they all have a valency of +1 , and p-block elements have according to their periods*(it's better to remember groups of p-block elements - these start from the boron group to halogen group (fluorine.)*
Chlorine has valency -1 and sodium has valency +1 so multiply them. The valency of chlorine will be the subscript for $\ce{Na}$ and valency of $\ce{Na}$ will be the subscript for $\ce{Cl}$.
Similarly, Mg has valency 2 and oxygen also 2 $\ce{Mg_2O_2}$ will be the compound since both subscripts are common, we generally don't write them and we write $\ce{MgO}$ as compound.
There are still lot of exceptions.
Hope this helped.