Textbook Question
Fill in the following blanks using larger or smaller, higher orlower. Mg has a atomic size and a ionization energy than Cs.
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9. Electrons in Atoms and the Periodic Table
Periodic Trend: Ionization Energy (Simplified)
Multiple Choice
Which element has the smallest first ionization energy?
A
Lithium (Li)
B
Sodium (Na)
C
Chlorine (Cl)
D
Potassium (K)
Verified step by step guidance1
Understand that first ionization energy is the energy required to remove the outermost electron from a neutral atom in the gaseous state.
Recall that ionization energy generally decreases as you move down a group in the periodic table because the outer electrons are farther from the nucleus and are shielded by inner electrons.
Identify the group and period of each element: Lithium (Li), Sodium (Na), and Potassium (K) are all in Group 1 (alkali metals), while Chlorine (Cl) is in Group 17 (halogens).
Compare the positions of these elements: Potassium (K) is below Sodium (Na), which is below Lithium (Li) in Group 1, so Potassium has its outer electron further from the nucleus and more shielding.
Conclude that among the given elements, Potassium (K) has the smallest first ionization energy because it is the lowest in Group 1, making it easier to remove its outermost electron.
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