Multiple Choice
How many electrons are present in an Al^{3+} ion?
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2. Atoms & Elements
Ions
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Which of the following best explains why the Na^+ ion is smaller than a neutral Na atom?
A
Na^+ has more electrons than Na, causing the ion to contract.
B
Na^+ has a larger number of energy levels than Na, making it smaller.
C
Na^+ has gained a proton, increasing its nuclear charge and shrinking its size.
D
Na^+ has lost an electron, resulting in a decreased electron-electron repulsion and a smaller radius.
Verified step by step guidance1
Understand that the size of an atom or ion is influenced by the balance between the positive charge of the nucleus (protons) and the negative charge of the electrons.
Recognize that a neutral sodium (Na) atom has 11 protons and 11 electrons, while the sodium ion (Na^+) has 11 protons but only 10 electrons because it has lost one electron.
Note that losing an electron reduces the electron-electron repulsion in the electron cloud, allowing the remaining electrons to be pulled closer to the nucleus.
Since the number of protons remains the same but there are fewer electrons, the effective nuclear charge experienced by each electron increases, pulling the electrons inward and decreasing the ionic radius.
Conclude that the Na^+ ion is smaller than the neutral Na atom because the loss of an electron leads to decreased electron-electron repulsion and a stronger attraction between the nucleus and the remaining electrons.
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