A chlorine atom forms a chloride anion (Cl-) by gaining one electron to complete its octet configuration. This results in a unit negative charge since the number of protons (17) remains the same while the number of electrons increases to 18.
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A chlorine atom forms a chloride anion (Cl⁻) by gaining one electron. Chlorine, belonging to Group 17 (halogens) on the periodic table, has seven electrons in its outermost energy level (3s² 3p⁵) and tends to achieve a stable, noble gas electron configuration similar to argon with eight electrons. In chemical reactions, chlorine readily accepts an electron to complete its outer electron shell, resulting in the chloride anion. The added electron gives chlorine a negative charge, and the resulting chloride ion has an electron configuration resembling that of a noble gas, making it more stable and less reactive than the chlorine atom.