Consider the elements bromine and chlorine. Which element has a higher first ionization energy?

• A. Neither has a measurable ionization energy
• B. Chlorine
• C. Bromine
• D. Both have the same ionization energy

Answer: (B)

Verified step by step guidance

1. Recall that the first ionization energy is the energy required to remove one electron from a neutral atom in the gaseous state.
2. Understand that ionization energy generally increases across a period (left to right) in the periodic table and decreases down a group (top to bottom) because of increasing atomic radius and electron shielding.
3. Identify the positions of bromine and chlorine in the periodic table: both are in Group 17 (halogens), but chlorine is in Period 3 and bromine is in Period 4.
4. Since chlorine is above bromine in the same group, chlorine has a smaller atomic radius and less electron shielding, which means its outer electrons are held more tightly.
5. Conclude that chlorine has a higher first ionization energy than bromine because it requires more energy to remove an electron from chlorine's smaller, less shielded atom.