Question

chemistry semester 1 exam on level 25-26
which sequence correctly places the elements in order of increasing ionization energy?
○ cl, f, br, i
○ f, cl, br, i
○ i, br, f, cl
○ i, br, cl, f

Explanation:

Step1: Recall Ionization Energy Trend

Ionization energy (IE) generally increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table. For halogens (Group 17: F, Cl, Br, I), as we move down the group (from F to Cl to Br to I), the atomic radius increases, and the outermost electrons are farther from the nucleus, so IE decreases. Thus, increasing IE order should be from the bottom of the group to the top (I < Br < Cl < F).

Step2: Analyze Each Option

• Option 1 (Cl, F, Br, I): Incorrect. F has higher IE than Cl, Br, I, but order is mixed.
• Option 2 (F, Cl, Br, I): Incorrect. This is decreasing IE (top to bottom), but we need increasing (bottom to top).
• Option 3 (I, Br, F, Cl): Incorrect. F has higher IE than Cl? No, F is above Cl, so F > Cl. So order here is wrong.
• Option 4 (I, Br, Cl, F): Correct. I (bottom) < Br < Cl < F (top), so increasing IE.

Answer:

I. Br, Cl, F (the option "I, Br, Cl, F")