In the fourth period of the periodic table, how many elements have one or more 4d electrons? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

# Elements with 4d Electrons in Period 4 **Step 1: Identify what "4d electrons" means** We need elements that have electrons in the 4d orbital. The 4d orbitals first begin filling in the **5th period** (starting with Yttrium, Y, atomic number 39). **Step 2: Check the 4th period electron configuration** The 4th period includes elements from K (Z=19) to Kr (Z=36). - Filling order follows: 4s² → 3d¹⁰ → 4p⁶ - Maximum configuration: [Ar] 3d¹⁰ 4s² 4p⁶ **Step 3: Determine if any 4th period element has 4d electrons** Since the 4d orbitals have higher energy than 3d and 4p orbitals, they are **not occupied by any element in period 4**. The 4d orbitals remain empty throughout the entire 4th period. **Conclusion:** **Zero (0) elements** in the 4th period have one or more 4d electrons. The answer is **C: 0**