When an atom gains a negative charge, it means that it has gained one or more electrons. However, it does not lose protons in the process.
In a neutral atom, the number of protons in the nucleus is equal to the number of electrons surrounding it, creating a balanced electrical charge. Protons carry a positive charge, while electrons carry a negative charge. This balance is what makes the atom electrically neutral.
When an atom gains an electron, it now has one more negatively charged electron than positively charged protons. This results in an overall negative charge for the atom. The nucleus, which contains the protons, remains unchanged, so the number of protons remains the same.
For example, a chlorine atom (Cl) normally has 17 electrons and 17 protons, giving it a neutral charge. When a chlorine atom gains one electron, it now has 18 electrons and 17 protons. The extra electron creates an imbalance, resulting in a negative charge. The atom is then referred to as a chloride ion (Cl-), indicating the gain of a negative charge.
In summary, when an atom gains a negative charge, it means that it has gained one or more electrons, not that it has lost any protons. The number of protons in the nucleus remains constant, while the gained electrons contribute to the overall negative charge of the atom.