Which element has a higher first ionization energy: potassium (K) or bromine (Br)?

• A. It cannot be determined from the periodic table
• B. Both have the same first ionization energy
• C. Potassium (K)
• D. Bromine (Br)

Answer: (D)

Verified step by step guidance

1. Recall that the first ionization energy is the energy required to remove one mole of electrons from one mole of gaseous atoms, and it generally increases across a period (left to right) and decreases down a group (top to bottom) in the periodic table.
2. Identify the positions of potassium (K) and bromine (Br) on the periodic table: potassium is in Group 1 (alkali metals) and Period 4, while bromine is in Group 17 (halogens) and Period 4.
3. Since both elements are in the same period, compare their positions across the period: bromine is to the right of potassium, meaning bromine has a higher effective nuclear charge attracting its electrons more strongly.
4. Because bromine has a higher effective nuclear charge and a smaller atomic radius compared to potassium, it requires more energy to remove an electron, resulting in a higher first ionization energy.
5. Therefore, based on periodic trends and their positions, bromine (Br) has a higher first ionization energy than potassium (K).