AP Chemistry: Atomic Structure & Periodicity 3 — Questions and Answers
Question 1: Across a period from left to right, atomic radius generally:
- increases
- decreases (Correct answer)
- stays constant
- first increases then decreases
Correct answer: decreases
Increasing nuclear charge pulls electrons in the same shell closer, shrinking the radius.
Question 2: Which element has the highest first ionization energy?
- Na
- Mg
- Al
- Cl (Correct answer)
Correct answer: Cl
Chlorine is farthest right in the period, giving it the highest first ionization energy among these.
Question 3: Why does oxygen have a slightly lower first ionization energy than nitrogen?
- Oxygen is larger
- Oxygen's paired 2p electron experiences repulsion (Correct answer)
- Nitrogen has more protons
- Oxygen has a full 2p subshell
Correct answer: Oxygen's paired 2p electron experiences repulsion
Removing the paired electron in oxygen's 2p^4 is easier due to electron-electron repulsion.
Question 4: Which element is the most electronegative?
- Fluorine (Correct answer)
- Oxygen
- Chlorine
- Nitrogen
Correct answer: Fluorine
Fluorine is the most electronegative element on the periodic table.
Question 5: The second ionization energy of sodium is much larger than its first because:
- It removes a core electron from a noble-gas configuration (Correct answer)
- Sodium gains electrons
- The atom becomes larger
- The nuclear charge decreases
Correct answer: It removes a core electron from a noble-gas configuration
After losing one electron, Na+ has a stable neon core, making the next removal very difficult.
Question 6: Which trend correctly describes electron affinity moving down a group?
- Generally becomes more negative
- Generally becomes less negative (Correct answer)
- Stays exactly constant
- Always becomes zero
Correct answer: Generally becomes less negative
Larger atoms down a group add electrons less readily, so electron affinity becomes less negative.
Question 7: Which cation is smaller than its parent neutral atom?
- Cl- vs Cl
- Mg2+ vs Mg (Correct answer)
- O2- vs O
- F- vs F
Correct answer: Mg2+ vs Mg
Mg2+ loses its outer shell and has greater effective nuclear charge per electron, making it smaller than Mg.
AP Chemistry: Atomic Structure & Periodicity 3
Across a period from left to right, atomic radius generally: