system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does chlorine (Cl) change so drastically from a gas to table salt (NaCl) when sodium is added?
gpt
When Cl is alone, it is missing only one electron so it desperately wants to find one to complete its orbital. That is why chlorine gas is so corrosive - it’s trying as hard as it can to yank electrons off anything it can find. 
Sodium on the other hand has one electron it desperately wants to get rid of. It donates it to the chlorine, which gives the Na a positive charge and the Cl a negative charge. The opposing charges make them stick together and they fall into a very stable, very regular pattern — the salt crystal! When all the Na and Cl ions are lined up in the crystalline structure, their charges are balanced on all sides. Basically they have everything they need, and so they are essentially non-reactive in that state.