 We use chemical equations as a symbolic representation of what happens to atoms during chemical reactions. Let's now look at how we can use them to more accurately represent processes that involve aqueous ions, ions that are dissolved in water. This type of equation is known as an ionic equation. An ionic equation is a type of chemical equation. We use it for situations in which aqueous ions exist in order to represent the fact that the ions are separated in the water and not stuck together as they would be in the solid version of the compound. A simple example, the dissolving of sodium chloride in solution, would be represented like this. When you're writing ionic equations there are a couple of things to remember. I'll run through them using magnesium bromide as an example. First, only substances that have separated into ions when they dissolved in water are written as separate ions. All other compounds are written as normal. That includes solid ionic compounds, undissolved or precipitated, covalent compounds, metals, gases. They're all written as normal. So if we represent magnesium bromide dissolving, the magnesium bromide on the left is shown as the complete formula because it's a solid and the ions are bonded together. While on the right of the equation the ions are written separately because here we're representing the fact that they've dissolved and have separated into solution. Second, as with any chemical equation the atoms must be balanced on the left and the right of the equation. Here we check that there's one magnesium ion and two bromide ions on each side. Notice that the stoichiometric coefficient of the bromide ions on the right hand side is a big two, representing two separate bromide ions. On the left hand side in the formula there's a small two that comes after the bromide because we're representing that there are that many bromides within the formula rather than separated out. Third, we have to show the charges on the separated ions. If I were to write this equation like this without charges it would be incorrect since plane mg represents a neutral magnesium atom when in fact it's a magnesium ion that we have here. Remember an ionic compound is made of ions in a lattice when it's in its solid form and those ions are still ions when they dissolve and separate in water. A little bit of a side note here when we write the complete formula of an ionic compound when it's a solid for instance we don't explicitly write the charges on the separate ions so mg-br2 there's no charges shown there. That's because the charges on the cations and the anions balance each other out in that compound to make the overall compound neutral. However when it dissolves in water the cations and the anions separate from each other and so they're no longer neutralizing each other's charge so when we show them separately we need to write them each with their proper charge. Fourth, in the same way that you balance atoms on the left and right of the equation you should balance the total charge on the left and right of the equation. Remember conservation of mass we can't lose or gain any whole atoms in a chemical reaction but neither can we gain or lose any electrons so whatever the total charge is that we start with on the left it should remain the same on the right. Here on the left we have the neutral compound mg-br2 so that's a total charge of zero. On the right we have two plus from the magnesium ion and two lots of one minus from the two bromides so that adds up to zero overall and that means that we have the same total charge on both sides of the equation. Doing this is a good way of checking for mistakes in your equations.