Net Ionic Equations

When two solutions mix and something new forms, not every ion present actually does something. Write the full equation, then break every strong electrolyte into the ions it exists as in solution. Some ions show up unchanged on both sides, same charge, same form, nothing happened to them. Cross those out. What's left, the ions that actually combined into a precipitate, a gas, or water, is the net ionic equation. It's the honest picture of the chemistry: the rest was just along for the ride, fully dissolved and unaffected.

The cloudiness you see when two clear solutions mix is a precipitate: cations from one solution paired with anions from the other to form a compound water can't hold dissolved, so it drops out as a solid. That's the reaction worth writing. Everything else in the beaker, the ions that stayed in solution before and after, are spectators, not failures to dissolve. A spectator ion is just as dissolved as any other ion present; it simply didn't change partners or form.

This connects directly to solubility rules, since you need them to know which product actually precipitates, and to acid-base and gas-forming reactions, where the same stripping-down process applies. Strong acids and strong bases split completely into ions, so they disappear into the net equation except for the part that reacts. Weak acids don't fully ionize, so they stay written as whole molecules, not as separate ions, because that's their real form in solution. That single change shifts which species counts as a spectator and which is the actual reactant.