Writing electron configurations for ions explained with examples

📚 Quick Study Guide

• ⚛️ An ion is an atom or molecule that has gained or lost electrons, giving it an electrical charge.
• ➕ Cations are positive ions formed when an atom loses electrons. Write the electron configuration for the neutral atom, then remove electrons from the outermost shell (highest principal quantum number $n$).
• ➖ Anions are negative ions formed when an atom gains electrons. Write the electron configuration for the neutral atom, then add electrons to the outermost shell.
• 📝 Remember the order of filling orbitals: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.
• 💡 Noble gas shorthand can simplify electron configurations. For example, potassium (K) is $[Ar]4s^1$.

🧪 Practice Quiz

1. What is the electron configuration for $O^{2-}$?
   1. $1s^22s^22p^2$
   2. $1s^22s^22p^4$
   3. $1s^22s^22p^6$
   4. $1s^22s^22p^5$
2. What is the electron configuration for $Fe^{2+}$?
   1. $[Ar]4s^23d^6$
   2. $[Ar]3d^6$
   3. $[Ar]4s^23d^4$
   4. $[Ar]4s^13d^7$
3. What is the electron configuration for $Na^{+}$?
   1. $1s^22s^22p^63s^1$
   2. $1s^22s^22p^5$
   3. $1s^22s^22p^6$
   4. $1s^22s^22p^43s^1$
4. What is the electron configuration for $Cl^{-}$?
   1. $[Ne]3s^23p^4$
   2. $[Ne]3s^23p^5$
   3. $[Ne]3s^23p^6$
   4. $[Ar]3s^23p^6$
5. What is the electron configuration for $Al^{3+}$?
   1. $1s^22s^22p^63s^23p^1$
   2. $1s^22s^22p^6$
   3. $1s^22s^22p^63s^2$
   4. $1s^22s^22p^5$
6. What is the electron configuration for $Cu^{+}$?
   1. $[Ar]4s^13d^{10}$
   2. $[Ar]4s^23d^9$
   3. $[Ar]3d^{10}$
   4. $[Ar]4s^23d^{10}$
7. What is the electron configuration for $S^{2-}$?
   1. $[Ne]3s^23p^2$
   2. $[Ne]3s^23p^4$
   3. $[Ne]3s^23p^6$
   4. $[Ar]3s^23p^6$