AP Chemistry Questions on Ionization Energy and Electron Configuration

🧪 Quick Study Guide

• ⚛️ Ionization energy is the energy required to remove an electron from a gaseous atom or ion. The first ionization energy ($IE_1$) refers to removing the first electron, the second ionization energy ($IE_2$) refers to removing the second electron, and so on. Generally, $IE_1 < IE_2 < IE_3...$
• 📈 Ionization energy generally increases across a period (left to right) due to increasing effective nuclear charge and decreases down a group (top to bottom) due to increasing atomic size and shielding.
• 🛡️ Shielding effect: Inner electrons shield outer electrons from the full nuclear charge, reducing the effective nuclear charge experienced by the outer electrons.
• 📍 Exceptions to the trend: Be to B (Group 2 to Group 13) and N to O (Group 15 to Group 16) are common exceptions. B has its highest energy electron in a p orbital, while Be has its highest energy electron in an s orbital. Oxygen forms a stable half-filled $p$ orbital when it loses an electron.
• 📝 Electron Configuration: Describes the arrangement of electrons within an atom. Use the Aufbau principle, Hund's rule, and the Pauli exclusion principle to determine electron configurations. Remember the diagonal rule.
• 💡 Hund's Rule: Electrons individually occupy each orbital within a subshell before doubling up in any one orbital.
• ➕ Ions: When forming positive ions (cations), electrons are removed from the outermost shell (highest $n$ value) first. When forming negative ions (anions), electrons are added to the outermost shell.

Practice Quiz

1. Which of the following elements has the highest first ionization energy?
   1. A. Sodium (Na)
   2. B. Potassium (K)
   3. C. Lithium (Li)
   4. D. Cesium (Cs)
2. Which of the following electron configurations represents an element with the lowest first ionization energy?
   1. A. $1s^22s^22p^4$
   2. B. $1s^22s^22p^6$
   3. C. $1s^22s^22p^63s^1$
   4. D. $1s^22s^22p^5$
3. Which of the following correctly ranks the elements in order of increasing first ionization energy?
   1. A. F < Cl < Br < I
   2. B. I < Br < Cl < F
   3. C. Cl < F < I < Br
   4. D. Br < I < F < Cl
4. Which of the following elements has the largest jump between its first and second ionization energies?
   1. A. Sodium (Na)
   2. B. Magnesium (Mg)
   3. C. Aluminum (Al)
   4. D. Silicon (Si)
5. What is the electron configuration of the $Fe^{2+}$ ion?
   1. A. $[Ar]4s^23d^6$
   2. B. $[Ar]4s^23d^4$
   3. C. $[Ar]3d^6$
   4. D. $[Ar]4s^13d^5$
6. Which of the following species has the highest ionization energy?
   1. A. O
   2. B. $O^+$
   3. C. $O^-$
   4. D. $O^{2-}$
7. Which of the following elements has the electron configuration $1s^22s^22p^63s^23p^3$?
   1. A. Silicon (Si)
   2. B. Phosphorus (P)
   3. C. Sulfur (S)
   4. D. Chlorine (Cl)