* Neon (Ne) is a noble gas with an atomic number of 10. This means it has 10 protons and 10 electrons. Its electron configuration is 2, 8. This arrangement of electrons is very stable, hence why noble gases are unreactive.
* Chlorine (Cl) has an atomic number of 17. This means it has 17 protons and 17 electrons. Its electron configuration is 2, 8, 7. Chlorine's outermost shell (the third shell) has 7 electrons, making it less stable.
By gaining one electron, chlorine's outermost shell will have 8 electrons, just like neon's outermost shell. This gives chlorine the same stable electron configuration as neon, making it more stable.
