Chlorine atom forms Cl- by

Step 1: Analyze the question We need to know how a neutral chlorine atom becomes a chloride ion (Cl⁻).

Step 2: The concept

• Chlorine is in Group 17 (the halogens) and has atomic number 17.
• Its electronic configuration is 2, 8, 7, so it has 7 valence electrons.
• Atoms tend to achieve a stable octet (8 electrons in the outer shell, like argon).
• Chlorine needs just one more electron to complete its octet, so it gains one electron rather than losing seven.

Step 3: Solution Cl + e⁻ → Cl⁻

• Before: 17 protons, 17 electrons (neutral)
• After: 17 protons, 18 electrons (net charge of 1−)

The extra electron gives the negative charge, and the configuration becomes 2, 8, 8, the same as argon.

Step 4: Check the options

• A. Donating a lone pair: this describes dative (coordinate) bonding, not ion formation.
• B. Gaining an electron: correct.
• C. Losing an electron: this would form Cl⁺, which is not what happens.
• D. Sharing an electron: this describes covalent bonding (e.g., Cl₂), which gives no ion.
• E. Sharing a lone pair: this is coordinate bonding, which also gives no ion.

Tip: Non-metals (like Cl, O, F) gain electrons to form negative ions (anions), while metals (like Na, Mg) lose electrons to form positive ions (cations). Remember: "Gain = negative, lose = positive." An easy trick is that "anion" sounds like "a negative ion."