Multiple Choice
Which of the following best describes how a negative ion (anion) is formed?
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2. Atoms & Elements
Ions
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When chlorine forms an ion, how many electrons does it gain or lose?
A
It gains 1 electron.
B
It loses 1 electron.
C
It gains 2 electrons.
D
It loses 2 electrons.
Verified step by step guidance1
Identify the atomic number of chlorine, which is 17. This means a neutral chlorine atom has 17 protons and 17 electrons.
Recall that chlorine is a halogen and typically forms ions by gaining electrons to achieve a full outer shell, similar to the nearest noble gas configuration.
Determine the electron configuration of chlorine: $1s^2 2s^2 2p^6 3s^2 3p^5$. Notice that the outermost shell (third shell) has 7 electrons.
Since a full outer shell for chlorine corresponds to 8 electrons (like argon), chlorine tends to gain 1 electron to complete its octet.
Conclude that when chlorine forms an ion, it gains 1 electron, resulting in a chloride ion with a charge of $-1$.
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