How is a fluoride ion formed from a fluorine atom?

• A. Losing an electron
• B. Sharing electrons
• C. Gaining an electron
• D. Gaining a proton

Answer: (C)

Forming a fluoride ion happens when fluorine gains an electron to complete its outer shell. Fluorine has seven electrons in its valence level and would be most stable with eight, achieving a full octet. By gaining one electron, it becomes F−, with eight electrons in the outer shell and a negative charge. This gain is favorable because fluorine has a high electron affinity and readily attracts electrons to form the negatively charged ion, especially in compounds like salts. Losing an electron would yield a positively charged species, which is not how fluoride typically exists in compounds. Sharing electrons describes covalent bonding, not the formation of an ion, and gaining a proton would change the element entirely.