Textbook Question
Why is the ionization energy of Cl lower than F, but higher than that of S? (4.7)
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9. Electrons in Atoms and the Periodic Table
Periodic Trend: Ionization Energy (Simplified)
Multiple Choice
Which element has the highest first ionization energy?
A
Na
B
He
C
Cs
D
Ne
Verified step by step guidance1
Understand that the first ionization energy is the energy required to remove one electron from a neutral atom in its gaseous state.
Recall that ionization energy generally increases across a period (left to right) on the periodic table because atoms have more protons, increasing the attraction to electrons.
Recall that ionization energy generally decreases down a group (top to bottom) because electrons are farther from the nucleus and experience more shielding, making them easier to remove.
Identify the positions of the elements: Na (sodium) and Cs (cesium) are in Group 1, with Cs below Na; He (helium) and Ne (neon) are noble gases in Group 18, with He above Ne.
Compare the elements based on their group and period trends: noble gases have higher ionization energies than alkali metals, and among noble gases, the one at the top of the group has the highest ionization energy.
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